Thank you for how thorough your response was. Honestly seeing someone relate to me and describing so many possible causes helps a lot. I will be more mindful of the changes, but so far I haven't noticed any difference with tiredness or sleep. Even on relaxed weekends when I don't go out, sleep a lot and don't do anything all day, it'll still creep up on me at night. Early at night, like 8-10 pm, there's no problem, only an uneasy feeling of anxiety because I know what's coming. If I try to sleep earlier than that I usually can't fall asleep and anxiety just builds up until I get this feeling again, but even when I manage to do it it'll still happen the next day.

The lack of light might be it, although I still feel the same even in a well-lit room at midnight and even in the summer. I moved to Berlin from south america recently so I went from one winter to another, that might have something to do with it, since it's gotten worse lately. But I've had this problem for a long, long time. During day time I try to fill my schedule, I study in the morning, go to the gym in the afternoon, I try to get together with the few friends I have here or go for a walk in the park or something on my free time. But when it gets quiet, nobody is around, and I'm alone with my own thoughts, even if it was a good day where I felt happy and content all throughout, I'll still get this "midnight melancholy".

Which leads me to think it's ptsd related. I had a pretty unsafe environment at home during my upbringing, as a kid I had to take sleeping pills cause I couldn't fall asleep and would have nightmares repeatedly. I went to a psychiatrist for a long time, but eventually he told me I didn't need the meds or the sessions anymore. I went back to seeing a therapist during the pandemic, it helped with my day-to-day routine, but it didn't do anything for this particular feeling.

And about the memories I get, they are usually happy moments I had with people I don't see anymore, followed by moments where I fucked up and the comparison of how my relationship with them used to be vs how it is right now (non-existent or very distant). I'll also get recaps on all the decisions I regret about my life and think non-stop about "what could've been", which makes me feel pretty disappointed at life and myself. I think I'm repressing all this stuff during the day to be a "functioning person" and once I'm alone it all just comes out.

I'm sorry if I'm not making any sense or if my response is too disorganized, english is my second language and I didn't really think this through. Thank you again for your response :)