I have felt similarly many times, about many things. I too tried to rationalise it in terms of symptoms, but it never quite added up - the worsening of symptoms from any given activity was often not bad enough to justify just how badly I DIDN'T WANT to do that thing.

I've been doing a lot of reading now that I'm well enough to do so, and came across a discussion of 'loss of executive function' as being very common following TBI. This is essentially a 'loss of ability to engage in purposeful activity' and can manifest as lack of motivation as well as problems with attention ie sticking to a task. It seems to basically be a mindset that makes you not want to do anything that is remotely difficult.

It came as a shock to me that I would have suffered from this as it feels kind of worse than my other symptoms, more of a change in who I am than just another bit of pain and discomfort. But I'm certain I had, and to an extent still have this symptom, and it sounds like you do too. It is common and should pass. Good luck!