hi there, your discription fits that of a bruise
which on get when blood clots
under the skin due to injury . You need not worry about it as the blood clot will be absorbed slowly in a week or 10 days. Before that there will be some pain and tenderness for a few days. The bruise is reddish brown the ferst 2 days then slowly changes colour to blue, to green to light brown and completely fades away. If you experience any symptoms of dizzyness
, or any episode of lightheadedness
or loss of conciousness or any other symptom then you will have to visit an ER and get an Xray of the skull and a CT scan
done. For now you can relax and not worry about it. You may take a painkiller to ease the pain. Some cold fomentation also might be helpful Take care.