I am sorry to hear about your friend. The problem becomes the possibility of the situation repeating itself. I realize he may not have fallen asleep because of bad work ethic or had any control over it because of the medication. This fact does not however change the fact that as a security guard his main job is to be awake and alert and as a result of his sleeping an issue could have arisen.The employer having fired him is not unreasonable and even with a doctors note the fact remains he fell asleep on the job. If he is off the medication he can attempt to talk to the employer and/or he can explain himself and hope for the bestLegally however it seems he might not have any real case. However I would advise contacting a local employment attorney who may be able to think of a possible loop hole that would help your friend.