Hi qwazy!
Since "Crashing" isn't a true medical term, it seems that everyone has a bit of a different definition. You might find this thread helpful: https://forums.phoenixrising.me/threads/crash-vs-pem-differences.87390/#post-2394288
I usually use the term to refer to a period where it took me longer than normal to recover. However, I may also say to my husband, "I'm crashing", meaning that I need to lie down this instant and may be down for the count for several hours.