Go see a doctor and listen to whatever they have to say once they get all the info.
Right now all you're doing is making a bunch of assumptions (X is going to happen) and sorta hoping that you choose changes that happen to be the correct solutions (so I need to do Y). That's not a good way to solve problems. But it's also not good for your mental health.
Keeping yourself going does not mean that you shoot out of bed at dead-o-clock in the morning and run screaming down the street at mach 5 for three straight hours after having eaten half of a pea. It is 100% possible to try too hard to go in what you think of as the "correct" direction with this stuff, only to make everything worse.
This goes for the mental/emotional aspect too. Yelling at yourself that you shouldnt ever do fun stuff EVER because that's not responsible or some nonsense is a fast way towards spiraling depression, and that brings even more fun problems.
Seriously: stop focusing on this stuff, and instead, simply take the practical action of making a doctor's appointment. See what they say, and then ask them: what steps can I do to be healthier and feel better?
THAT is going to help you.
As for the insomnia thing... ever thought of seeing a sleep specialist?
Also:
A lot more physical activity combined with some heavy duty fasting is necessary in my case.
Ye gods, no, dont do this.
Jumping from "standing still" to "ENGAGE WARP DRIVES" is *really* unhealthy. But again, if you push yourself too far, you'll just make everything worse. You'll entirely undo all of the benefits that your actions are meant to bring.
Trust me, you'll end up regretting that one really, really hard.
Again: Doctor appointment. Professional advice, professional solutions. That's what'll help.