Hit the back of my head two days ago, no signs of concussion, went to the er, doc said i was fine. however, afraid to fall asleep, am i safe to?

Probably safe.: The first 24 hours after any head injury require frequent evaluation (usually every 2 hours) for signs of head injury. If you have not had any symptoms of concussion, you are likely fine. However, there can be delayed consequences up to a month after, but this is rare. Not sleeping will certainly not help. If you have symptoms of concussion later get seen. No contact sports for a week, minimum