what exactly is autistic burnout?

what are the symptoms and mindset and any other relevant info?

ive been working as a volunteer warehouse assistant and also filling in on shop floor and elsewhere as needed, every day of week, from before opening, until closing, usually 9am - 6 pm, 11am - 5pm sundays, by choice i must add, so im just wondering if theres any signs i should look out for? again i feel i must state im awaiting asd assessment. cheers.