Hi Post-concussion symptoms are common after head injury and are diagnosed by exclusion of other complications following head injury. I suppose the CT scan has already been done in your case. The most frequent complaints that you may come across are: drowsiness, intellectual impairment, headache, dizziness, visual disturbance and vomiting. It is actually reduced short term memory and impaired concentration that makes it difficult to resume work. In case your baseline tests for memory, reactions etc are normal as you have said , then you do not have anything much to worry. The anxiety and precautions followed by your trainer is understandable. Yes your physician can give a written note but at the same time I suggest precautionary measures are always advised from medical point of view ( for a brief period) to prevent any neurological worsening . It is more so in your case as you are a player and prone to such injuries.