According to this video below, it seems my friend got the purpose somewhat right and somewhat wrong (although the video is Korean shamanism rather than Tibetan).
As mentioned, my friend's sister sent them to me on a chain with smaller bells, as a "new mother" gift - but the attached card was lost with the gift.
Thus, I had no idea there was actually supposed to be some 'mystical purpose' for them, I thought it was just a cool-looking, artsy necklace - so there's no way what happened was power of suggestion or imagination.
Besides, I was an atheist/agnostic at the time - not anymore, partly as a result of this experience lol - not knowing what to do or what was even happening, that night, I prayed - because as they say, there are no atheists in foxholes ;)
Plus my little sister witnessed it, although she admittedly was smoking too much weed at the time, so she barely remembers this event (or any events, around that time, other than the actual day my daughter was born) lol. She never smoked it in my house, though, and was not high that night, as she was there to help with the new baby.
I, of course, did not smoke weed at all.
Not only was I a new mother, but I never smoked weed much before that anyway, even in college.
Though it's supposed to chill you out, I always found it had the opposite effect, particularly increasing my social anxiety - which they've found is a common of THC on people with social anxiety. (In fact, the last time I had ever even tried smoking weed was a few years earlier, and I've never smoked it since).
Also, though my little sister and I don't always see eye to eye, she has a very good sense of humor, that's one thing we have in common - but neither she, nor I, would ever pull a mean prank like this on anyone, plus she heard it just as loud as I did and became as freaked out by being unable to explain it as I was.
(My older sister might, would, and has, and though doesn't have much a sense of humor, she's just mean - but that's another story lol. However, she was nowhere around - in Chicago, in fact lol)
Okay, so after reading this morning about varying purposes of shaman bells (I couldn't find much), it is common to give them to pregnant or new mothers to help both warn the mother about evil spirits/negative energy and also chase them away, so my friend was right about that - but what she didn't know is that there's cleansing ritual you're supposed to do along with them - which is explained on this video.
This would explain why they only rung/rattled on their own when I was in the room, only around me - and why my sister heard them just as loud as I did, when she laid down in the bed next to me - because the original shaman "blessing" was for me, as a protective new mom :)
Also, here's more about the reason they only rattled when my sister and I were drifting off to sleep, the stage between arousal/non-arousal - AKA the "Theta" (also known as "alpha-beta") waves, named for the brain-wave pattern that occur while "falling asleep" or during meditation on EEGs (electoencephalogram - an electronic method of monitoring brain waves, typically used for people suspected of seizures).
The Theta-wave state is spiritual state that shaman seek to enter in ritual - a heightened state of "awareness," while the body itself is completely relaxed so as not to distract the body. It's also the state hoped to achieve with meditation and/or prayer.
So, the Theta brain-wave state has its own separate pattern, already proven to exist on EEG (see above) - but now we know what this looks like on SPECT scan imaging (though there are slight differences in SPECT scans between actually falling asleep VS self-induced "theta" states through meditation/prayer.)
The below are SPECT scan images of people fully awake right before meditation/prayer, and the second image is actually during meditation/prayer.
Red is a hyper-aroused brain - active thought, analysis, judgment of stimulus.
Yellow is brain awareness or orientation - when your brain is essentially just receiving information and observing without analysis or judgment. Your brain "standing at attention," waiting to receive information - receiving input only.
Note the frontal lobe portion of the brain that is associated with orientation/attentiveness/awareness lights up in a specific "yellow" pattern - the area of your brain associated "orientation" or "attentiveness" flips to yellow or "reception" mode.
If you've ever meditated, then you know the goal of meditation is to NOT analyze/judge, but also not "stop thoughts" as they enter - just allow them to flow in and out, by not placing analysis, judgment, or action on them - and the body relaxes as a result.
However, at the same time, the body itself is completely relaxed, so as not to distract the brain from its attentiveness.
Interesting stuff, huh?
No, it is NOT a "trance" state - it's a natural state of the brain between wake and sleep that occurs anyway, when you go to sleep - the brain's way of opening up to receive as much input as possible, without being distracted by the body - only intentionally induced.
Thus, the reason shaman seek to enter this state is it's the time the brain is supposed most "receptive" to spiritual information, even communicate spiritually, and not be distracted by the body or other stimuli.
So that would explain THAT aspect of the bells ringing only at that stage for myself and my sister.
Back to the bells, in other words, you can ring them on their own to chase negative energy/"evil spirits" away - but you have to know what you're doing, the ritual.
When they ring/rattle on their own as a warning, like they did that night - that cleansing ritual must follow, to chase away the negative energy/"evil spirits" - and it either must be done by a shaman themselves to chase it away or the shaman must teach you - and the ritual can take days.
They also might ring/rattle if you are a 'natural' shaman, but then you still should probably find out what in the heck to do (which I didn't, until now - 25 years later, after I threw the bells out, stuff like that freaked me out at the time, rather than intrigued me, like today lol).
What's a "natural" shaman?
A person who is naturally gifted with spiritual sensitivity or a highly intuitive, empathic person.
We might call this person a "psychic," or in Christianity, some might say they the "gift or prophecy" or "gift of discernment" (Acts Chapter 2 delineates spiritual gifts available). Tribal people, however, just call such people "shaman" - and in most cultures, they can be male OR female.
However, in most tribal religions, this person becomes this way as the result of trauma, particularly surviving near-death trauma.
As a result of suffering but being left alive, they now have one foot in the physical plane and one foot in the spiritual world for the rest of their lives.
Thus, interestingly, trauma and suffering are revered in tribal cultures; experiencing great suffering, but being left alive, is an honor, it sanctifies you - it brings you closer to God - if you allow it to :)
(Yes, even in tribal cultures, there's free will and choice of what to do with your suffering - let it destroy you or empower you.)
This is opposed to our Western culture who often blames the individual's "sin" for their own trauma and suffering and stigmatizes it, rather than embracing that trauma and suffering can be used as a conduit to enlightenment and being closer to God :)
Though I am a practicing Christian, as mentioned, I believe all religions have some positive wisdom to contribute - and I personally believe this concept of suffering and sanctity is what was actually meant by our scripture, as opposed to what churches have made it become.
In fact, though I'm not Catholic, I'm Episcopalian (watered-down, liberal Catholic), this is one area I think the original Catholic doctrine got right - suffering sanctifies and brings you closer to God - it's how their saints are made :)
Unfortunately, especially in the Catholic faith, that concept somehow got lost when it came to especially sexual/reproductive sin, shame and bringing bad things on yourself, which is actually contrary to their own doctrine, and is actually based on residual OT law more than anything else ("thank" Paul the Pharisee Pleaser for that) - but it actually doesn't gel with either Christ's New Testament message OR original Catholic doctrine.
Regardless, my point is, no religion is pure and unfiltered, they've all incorporated other beliefs in their texts already, from the beginning - and Christianity is no exception.
We've often incorporated other faiths into our scripture - Zoroasterians (the wise men, astrology and numerology - saying things 3 times appears much in the bible), as well as the Old Testament law is largely "borrowed" from Hammurabi's code and the Sumerians in Babylonia, and the Israelites were captives at the time). And let's not forget our beloved Christmas trees are actually Pagan in origin ;)
Additionally, we have most likely interpreted things from Aramaic, Hebrew, and Greek completely wrong, and this is proven by the fact that even the most education Christian scholars, associated with a church or not, do not cannot agree on how to interpret these ancient languages accurately and adequately.
So it's quite possible that the intended message and what we ended up with, in some Christian texts that seem to contradict others (even contradict Christ) weren't from God or Christ at all, or we misinterpreted them (intentionally or otherwise) - and I believe that the concept of suffering is one of them.
And what's interesting is, some form of these bells exist in all cultures in some form - even our own Christian faith has a "supernatural" reason we ring bells of "consecration."
Regardless, as I said, I'm an atheist no more, partly as the result of this unexplained experience - and I've also learned, and please be advised based on this experience - ya probably shouldn't mess with stuff like this, or give them as gifts, unless you know exactly what you're doing ;) lol