Exercise minimums, for those with health troubles?

I have a lot of health problems I have been dealing with lately.... Besides some of the usual troubles associated with being overweight, (Knee problems, asthma etc...) I also have some extra stuff I'm dealing with.... head problems, like dizziness and balance problems, head pains and even fainting spells which I haven't been able to get successful help for yet...

Since joining I've really been making an effort to exercise as much as I can, whenever I can, however while I have my good days, I also have bad days, where I'm unable to leave bed.... And then I have my middle-days, where I can do *something* But not very much...

Up until now when entering exercises, I've added walks or shopping trips, light dance aerobics on my very good days.... things I can at least enter in a minimum of 15 minutes for... (Though I have gotten them over 1hr on occassion)

Here's what I'm wondering though.... For the times when I'm having my not-so-great days... While I'm not able to go walk a few miles or do a 20 minute dance workout... I think of "little" exercises I can do, crunches or leg lifts, just really basic stuff.... But I feel really discouraged because I can't do very much of it, on those days, and it doesn't seem like anything worth recording in my exercise diary...

What do you think? are 5 minutes at a time of some of the basic exercises worth recording? Maybe they can add up through the day? Or should I just do them on the side, and not record them, but just be satisfied I'm doing something "extra" .... Or perhaps I should save up whatever energy I have for the longer workouts that actually mean something?

Is anyone else dealing with health troubles too that really limit what they are physically able to do as far as exercise? How do you get around this obstacle?

I find it very difficult to find a safe balance with exercise... the small stuff seems so little, especially when I want to do more, that I get discouraged and don't want to do anything at all... and then when I do something finally, I have a tendency to go overboard and mess myself up for a few days....