My question is: As I am 68 years old but do not look like that, I am a 'fighter' and demanding ( lots of?

I don't know where this post belongs Barb. It landed here in martial arts because you used the term fighter, try to select the section yourself.

Uh?

You are 68, that means you are a senior citizen, even if you don't look it, you are, so you must be careful.

If you feel week, check your diet, exercise, sleep, etc. and go see a doctor.

Also, there is one thing for sure:

This has nothing to do with martial arts.

Good luck!