Tyla Grant, 24, holds down a full-time advertising job, is trying to get a nonprofit off the ground and creates regular content for her podcast, YouTube channel and Instagram. Occasionally, she winds up so fried she can’t speak or get out of bed for days. Ms. Grant is also autistic. While most people undergo periods of burnout — physical, cognitive and emotional depletion caused by intense, prolonged stress — autistic people, at some point in their lives, experience it on a whole different level. Though little studied, burnout among people with autism has become its own pandemic.