yes, this usually happens to me when my stress levels are high and i just can’t cope. stress kinda snowballs into so much more negativity in my mind

like cloudnine said, life stress is often the culprit, but it's also possible you have an unknown or subtle trigger. i definitely don't know all of mine - recently i learned that being cold indoors is a trigger for me and i never would have guessed it. and i've noticed that my partner has absolutely no clue about their triggers, even though i notice them

Yes! Ive chalked it up to my brain just preparing itself for what it thinks is oncoming danger. When your childhood is so chaotic, times of peace will feel nice, but then put you on edge. Bc peace in my childhood was just a break until things got awful again. Idk if this might be the case for you. You also may have gotten triggered but chose to forget the trigger at the time, or don't realize it affects you that heavily.

Yes. Unfortunately sometimes there is no known trigger. Something as subtle as a smell or a noise could do it. Out brains are weird in that way.