For over two years I ran a low grade temperature that caused a headache. I did not particullarly care if I ate. All I wanted to do was sleep. And yes, I fell asleep in class and work. The problem was my tsh levels of my thyroid. The normal tests for thyroid showed that there was nothing wrong with me. Even the endocrinologists did not think I had thyroid problems until the tests came back. I have hashimoto's hypothyroid disease. You may want to be tested for this.