I was walking outside and i slipped on ice and hit my back and head super hard currently have a really bad headache and the back of my head hurts i also didnt remember where i was after i fell (but that could be mental illness related?

Although in absence of more information, it is tough to be precise, I would gather most likely, that you suffered a concussion and a scalp hematoma over the posterior skull. Post-traumatic headaches are common. Would contact your doctor if headaches worsen, nausea and vomiting, blurred or double vision, dizziness or gait imbalance, or periods of loss of consciousness.

Retrograde memory loss with concussion, losing the memories formed just prior to the trauma can be seen when the brain is jarred within the skull cavity. Symptoms can last for a while, even though often when neuroimaging is obtained, it is normal. Be followed by a health care professional, your primary doctor for sure, if not a neurologist