If this is a mitochondria issue why don’t our organs stop functioning

Some people who don’t know they have me/cfs yet continue to push themselves to live a normal life. That was me, the first 6 months of having it I had no idea what was wrong was me, so I continued working out, going to school, etc. I felt horrible but still managed to do it. Mitochondria are essential for keeping your organs running, so why don’t they just fail if you keep pushing yourself considering ur just going to deplete all your ATP?