Don't wait until you are thirsty. Drink a mouthful of isotonic drink every 10 to 15 minutes minimum regardless of how you feel. Same for nutrition. Take a protein recovery shake immediately after you work out and then eat your meals normally. Also drink plenty of water after you exercise.
Maybe I wasn't clear about this: I don't know how to maintain a consistent intensity when exercising. I don't have any particular awareness of my heart rate or respiration rate going up unless I stop and literally count. I don't have any sense of how fatigued I am until a good 15-30 minutes after I'm done, and even then it's quite vague.
As I already tried to explain upthread (this seems to be a pattern), I have tried, and I don't know how to do those things at the same time. I can stop and count my breaths, but the sensation is so indistinct that it becomes difficult to keep track of when I'm doing anything else.
1) I don't feel anything interesting during exercise. I feel vague pressure and tension in roughly the expected places for a given movement, but that's about it. I don't get the sense that my body is actually doing anything in response to that movement.
2) If I make any attempt at actual intensity instead of literally just going through the motions (which does not do much to alleviate point #1), I often end up with some weird injury that flares up over the next week or two, even when nothing seemed to go wrong. Getting "brain fog" for hours after the exercise is also pretty common.
I suspect this is something to do with a broader interoception deficit (I also have trouble gauging hunger/fullness, thirst, tiredness, illness etc.), but it's hard to find any reliable information about that sort of problem. Most sources basically just tag it as an autism spectrum symptom and don't bother actually examining it.