Going to the gym has recently been my de-stress activity. Get some good music on, go through your routine and hit the sauna after.

FeelsGoodMan

Stop competitive online play..... that wont do you any good if you dont like stress.
Stay with rewarding single player experiances, that you enjoy to play.

"The Witcher 3 has become less fun and is beginning to feel like a punishment, a chore I have to endure before I can move onto anything else."

Thats when I usually move onto the next thing, and just put it into a "get done at some point" pile. If gameing feels like a chore, its not healthy or fun.

De-stress & cheer-up?
Long warm baths,
takeing your time and enjoying good meals (it can be fun to try new recipes too)
and I rather enjoy reading a good book too, just snuggle up under covers, layback in bed, and relax with a book.

Watching Anime, Reading Manga and walking listening good music and Podcast every day.

If you want to de-stress, you should do things that aren't intensive for your brain. Doing sport (or just going for a walk) works great. Fapping too.

-Listening to music is the best for me. (If you see some weeb looking person with headphones listening to Persona 3/4/5 music, that's probably me.)

-Watching anime while at home is something I've been doing recently. (Just waiting for the next episode of BNHA.)

-Doing homework at a snail's pace at a quiet environment like the library actually helps calm my nerves a little and helps to make sure my brain feels active.

-If all else fails, I fap to Futaba Sakura.

1. White Russians & Cape Cods
2. Old video games - Twisted Metal 2, Flower, Journey, Sonic the Hedgehog, E-SWAT.

https://www.humblebundle.com/hunie-sakura-bundle#heading-logo

...but aside from that, I study philosophy (right now: stoicism), and languages (Finnish).

Go for walks, that seems to be pretty effective. But I don't worry very much.

Also I'm not sure if this will work with you, but think of this (because I don't what your issue is). Will the problem matter in 5 months? 5 years?

Bristow9091 try getting more sleep too.
It sounds weird, but theres a link between sleep (less) -> stress (more).

Take the time you need to rest properly for a month or so and see if your stress isnt better from it.

Walks, play civ 5, anything Nintendo, work...