A very close friend of mine has changed a lot in the past few months. It seems as if he looks at everything with suspicion. He is always thinking about something. He forgets simple things and it looks like he's high even when he is not. He tries to cut off from everything around him. Whenever someone talks to him, he doesn't respond immediately. It is as if he takes 5-10 seconds to realise whats going on around him. I know for sure he's not doing it deliberately and he denies the fact that his mental health has deteriorated when each and everyone around him believes otherwise. Should we be worried ?