This question sounds to me a little like dieting: we know what is good for us, but sometimes we just want to say 'fuck it' and eat chocolate cake.
This translates into a sort of good vs. bad thinking, which is very black and white, and not really the way the world actually is. It sounds like you're saying that being physically active and living outdoors is "good" behaviour, while sitting around in your underwear playing video games and binge watching shows on netflix is "bad." This is the sort of thing that our minds love to do - set up dualities in the form of extremes. It must be especially hard for someone who's used to being watched in some way, i.e. surrounded by people at work, and you are afraid that without the outer control (which all jobs have, either overtly or subtly) your willpower will go out the window and you'll do whatever you want, regardless of whether or not it's good for you.
I used to be a dieter so I've explored this mindset quite a bit. The thing I found most helpful is to really listen to what I want in the moment - to be mindful of my own motivations and thoughts. Do I really want to eat a giant piece of cheesecake for breakfast, or am I only thinking about it because it's "bad" for me and forbidden? What if it wasn't forbidden, can I just eat it and enjoy it? If it's the former, then I don't eat it. If it's the latter, and I let go of the 'bad' label, then I'll eat it and enjoy it. Either way, it's not about willpower or control. It's learning to ask - What do I really want? vs. What is my ideal that I want to move towards, and what am I afraid of that I want to avoid? The push / pull thinking gets me into trouble as it adds a layer of mental conflict to the situation that should really be quite simple.
Once you understand this dualistic thinking, and really pay attention to the tricks you're playing with yourself, then it dissolves. In your situation, if it means allowing yourself, giving yourself 100% permission and freedom, to play video games whenever you want, then you will be killing off this sort of good-vs-bad thinking. Eventually you'll feel like you actually want to go outside and be more active. Or, you may find that the sloth life is pretty boring. Or maybe it's something you NEED to do to decompress for a while. Just give yourself permission, and do what you want to do, without turning it into a mental conflict. It's the mental conflict that makes you unhappy, not the things that you're choosing to do.
In other words: you will have a choice to fill your day in whatever you way you need or want to at the time. Don't be afraid that you'll make the so-called 'wrong' choice. There is no wrong choice. Just trust yourself to make the choices that are best for you at the time, without inner judgment. You'll be a lot happier, and you'll find that life is not actually going to turn into a downward or upward spiral, as you're currently imagining it. There is a massive grey area in between.