I have the exact same problem, and I do think that it is connected to autism. Since I have started leading a more active lifestile, my energy requirement has almost doubled, and it actually had a benefitial effect on my eating habits. Whenever I get really tired for some reason, and I don't know why, I think: Oh, it has been a while since your last meal. Go eat something. The thing is, whenever I do something I have really lost myself in, I forget all other feelings. I actually think that this is a merit that will, in later life, attract potential employers to my qualities as an employee: Give me a task, set me behind a desk with all the stuff I need, and I go for hours and miles without stopping... I have made sessions in the college library lasting 8 to 12 hours without taking longer breaks than 5 minutes for a quick eat or toilet. I am getting off track, but the idea is: Us with AS, we either get lost in our special interests, or we are overwhelmed by our surroundings, and our senses are always in a state of slight sensory overload, so we phase out and cannot perceive ourselves and our own bodies. I think it's the same reason why Aspies tend to be clumsy and bump into things and other people.