"I hit my head really hard but I wasn't knocked out, does someone have to wake me up several times tonight?"
Even a moderate blow to the head can cause a mild closed head injury. The idea of waking someone up periodically through the first 24 hours is so that their mental status can be briefly assessed and if there is a clear altered mental status such as confusion or extreme difficulty waking someone up this can be discovered earlier and that person can be brought to the Emergency Department for testing sooner than later. Many people in different contact (and non contact) sports will "have their bell rung" which may constitute a mild concussion.

"I got knocked out today and now I feel sick to my stomach."
The classic concussion includes loss of consciousness for seconds to minutes followed by nausea, confusion and some memory loss. If you were knocked out you should be evaluated immediately and maybe even kept and monitored in the clinic or Emergency Department. Often a person who has been knocked out will get a head CT scan to rule out any bleeding within the brain.

"My neck feels stiff since I got hit."
Approximately 5% of head injury victims suffer cervical spine (neck) fractures. A sore neck is to be expected especially the next day and if you are at all concerned about a fracture proceed to the nearest Emergency Department for an evaluation. Trauma of the head and neck are nothing to fool around with.