Hitting head hard on ground what should i do?

Go to ER if...: I assume you mean that you fell and hit your head on the ground. If so, as long as you don't take a blood thinner, had no loss of consciousness, vomiting, confusion or severe headache, you should be fine. If you had those things, or have a laceration or depressed area of your skull, go to the ER to be evaluated in person. You may, or may not, need a CT scan. Let the doctor decide.

Head trauma: If you hit your head hard, it is best to seek medical attention. Signs of concussion - nausea, headache, confusion and require immediate attention. If you hit it hard enough you should also watch for late signs a month later of a slow bleed called a subdural hemorrhage.