I took 50mg (10x 5mg pills) once out of curiosity.
It didn't make me any more tired than normal... I fell asleep quickly, and although I slept for a long time, it was not a good sleep; I was extremely tired and very disoriented in the morning. I didn't remember any dreams at all(as opposed to vividly remembering very colorful and wacky dreams) and I woke up a few times during the night with my eyes burning and completely bloodshot, and a strong feeling of pressure in my head.
Anyway it wasn't worth it, but I was fine the next day. I have 3mg pills now and you don't need any more than that