General anxiety disorder

It always looked like that my cousin Sean worried a lot and was a worrier. He often felt uneasy and restless he couldn't relax. At times it would come and go just like that, in seconds. But then it would be there constantly, series of thoughts and emotions. His behaviors wouldn't stop for hours even for days. He would constantly worry and for minor things "would he like the gift","will people like the shirt i have on." For him it became difficult to let things go and move on and would easily be scared. Restlessness and sleepless nights was his usual things. There were times when he would wake up middle of the night sweating and trembling for no reason at all. He was an active person but would loose track of what he was doing. He would read and forget he was reading. At time he would feel light headed and his heart would start pound rapidly. Just hearing his hear beat fast would make him worry more. Sean would always imagine things worse than they really seem to be. He often missed school and work, and it seem there is nothing he can do he would worry more when he misses both. Doctors told him they cant find nothing wrong internally and say that its stress.