Stopping doing something that causes harm is not giving up - it's being rational and realistic. The fact that exercise can cause harm goes against norms that everyone has absorbed and are even ingrained in sayings like 'hard work never hurt anyone'. Pacing and resting take a huge amount of willpower, and some people find that dietary changes do too. We are constantly fighting the urge to do more. That is not giving up! To avoid PEM you need to reduce activity, pace it carefully, go more slowly than you would like to, switch between different types of activity (e.g. from using your arms to using your legs to using your brain), and resting any part of your body - or your brain - when they feel fatigued. It's hard, and it never stops being hard, but it does get a bit more instinctive with time. Many of us also find that diet and supplements help, and you can find info on these in the relevant forums. I have found that with the right diet and supplements my excess fat has been replaced by muscle, so that I am stronger and can do more.