It's hard to always stay in the energy envelope and regularly I push too much and get PEM (which for me is feeling horribly sick with 9/10 pain level headaches). Even after 10 months of this I still haven't figured out exactly how long the delay between the activity that triggered the PEM and the PEM onset. Activity A Rest time A Activity B Rest time B PEM onset Sometimes if rest time B sounds like my normal PEM delay I'm surprised because Activity B may be small even for me. I guess it's more of a running total or "battery level" than the difficulty of a particular activity. Kind of a hard question given the energy envelope varies and the recovery rate also varies. To simplify the question, starting from a very rested state, if you perform an activity that obviously exceeds your envelope, how long until the PEM kicks in?