Im not in a good place atm either Chewy, but I think I can still give you something.

The obvious is that your mother passing is a terrible loss for you i'm sure, and things like that don't have set timetables for when its supposed to hurt the most or mess us up. Your video game addiction stuff I really wouldn't worry about, I'm young and a gamer too and honestly when I am not depressed video games take up most of my nights as I game with friends or whatever. While I am depressed those same games disgust me and make me think im a useless scumbag, but thats a symptom not a truth. One thing I think you should take into account is your drug usage this summer with your brother. Personally, I dont care about what drugs people use legal or illegal. In fact, you say after this party summer you felt invigorated to do well in life, so who is gonna argue that your cocaine etc usage is the entire reason your struggling now? No one sane imo. But just consider the following: Huge loss (mother dying), opens up a feeling of "offness" and sadness, went to Germany so a lot of brain stimulus there seeing your grandmother after your mother's passing, come back still being a bit "off" both psychologically and probably chemically in the brain, then go on summer vacation and blast your head with brain altering alcohol/drugs- plenty of stuff there to suppress some things, come back with a new plan for life-another major life event. So basically since your mother passed, you have filled your brain with either events or thoughts or distractions all of which aren't the most boring I would say.

Now you are depressed, and I say that not being a doctor. But you say you don't get enjoyment out of your usual stuff you like which is symptom #1 in depression. Your sleep is off, thats in the top 5 symptoms of depression. So hey man, you are depressed . But I think in your case its your time to be depressed. Maybe its your brain catching up with your body. Your mother passed and since then you have been doing so much (in my opinion) positive stuff. Sure Sure you probably could have done better without the cocaine and speed lol but whatever it was done and no permanent damage happened. So you want to know how to pass the time in your current rut or depressive episode, and all I can say is there are three things that I would do in your shoes.
1. Do not try to ignore or suppress emotions that may be about your mother's passing or that type of stuff. If it's anger, find some pillows or a punching bag and beat the **** out of it while your cry, if its sadness, cry your damn guts out, if its guilt or grief, more crying and also self forgiveness. LET IT OUT.
2. Maybe see a therapist? Again not a doctor, but if you go see a psych or maybe even a regular family doctor they are gonna write you a script for an Antidepressant. See a therapist first and if things aren't getting better or if you have ANY self harm thoughts, then go find a medical doctor for some help. I take antidepressants, in fact ive spent 9 months now looking for the right one, but honestly most people do it backwards and see a doctor before a therapist for emotional issues. Do it in the correct order.
3. NOW is the time to stay away from the drinks/drugs. If you are a cig smoker whatever you get enough preaching from TV commercial on why its bad for you bla bla. Forget that. But its well known that alcohol's effect on a depressed mind is an ugly one. If you are feeling good enough to have a beer or 2 or 3 with your friends one night, its not going to kill you, but if you self medicate with alcohol to try and ignore your bad feelings you are in for the nightmare of your life. The drugs ide just stay away from for now period. Your brain is going to be a chemical stew enough going through this without you giving it some cocaine to deal with as well lol.

So ya thats it, simple probably obvious stuff man. In my completely non expert and barely even amateur opinion, you need time, self help, and maybe therapy. If you want some good news, I would argue that your current depression is not an indicator of any kind of long term chronic depressive illness like me and many others on this site have. I say this in a positive way, although it sounds kind of negative lol, but you my friend have the right and good reason to have some depression in your life for a little bit. It will pass.