Well... I have to say this sounds a lot like me as well. Personally I chalk it up to a combination of depression & old age. I spend the majority of my time on-line... much of it here on PC.

And then, during the evenings, I typically watch TV with my wife because that's what she likes to do. We do have a dog we have to walk a couple of times a day since we have no yard for him to run in. There are other things I know I could be doing. But I just think... what's the point?
The problem with this sort of thing, of course, is that the more one does (or doesn't) do this... the less energy one has to do much of anything. It can become a downward spiral, so to speak. So I do make a point of not allowing myself to sink totally into oblivion.

One of the things that is most helpful to me in this regard is to have a routine. I pretty-much do the same things day-in & day-out. I don't always do them at exactly the same time. But I do them. And having that routine of things I do every day, keeps me from just veg'ing out completely.