During basketball i fell and slammed my head on the floor, had dizziness for a few minutes and how i have a stiff neck. what can i do, what is it?

You or someone else?: Hi. I recall some of your prior questions. If you have another health problem, please add it as a comment below if possible. In general, anyone with such a fall should contact a local doctor or go directly to the emergency department. I will refer this to doctors in related fields.

Head and neck injury: When one strikes their head on a hard surface and experiences dizziness and neck symptoms, i always get concerned about a head injury (subdural bleed, concussion, etc.) and a neck injury (cervical spine fracture, slipped disc, strain, etc.) although some of these are unlikely, they certainly are seriousness enough to deserve medical attention. See your doctor, go to the er, or call 911 if severe.

Get evaluated ASAP: You may need x-rays of your cervical spine or other imaging. There are some signs that can be reassuring, such as having a full range of motion at your neck. But there are many details of how you fell (flexed, extended, falling on top of your head..) that increase risk of an unstable vertebral fracture. Bottom line is, don't take chances - be seen by physician without delay!