Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. It may be due to primary syncope associated with head injury and seizures. Other possibilities, like atonic seizures followed by loss of posture then secondary generalization etc. Until examination is done it is difficult to say what it is. He may need secure air way. Protect him from sharp objects around him and maintain oxygenation. Please take him to neurophysician for further treatment, he will do CT scan brain with blood investigation and then treat you accordingly. Take care.