TIL about exploding head syndrome, which causes patients to hear a loud, frightening noise when falling asleep or waking up. Up to 10% of people may have it, but cases often go undiagnosed
Mine goes ShhhhshhiINNKK!!! Starts kind of static like and within the same second makes a sound like if you flicked a really thin glass really hard, but with a metallic finish. I also see a flash of purple/green/silver color on my eyelids when it happens.