Lately I have been feeling really numb and empty inside myself. I tried to think about something pozitive, about being with my girlfriend and cuddling.  So that I can get out of this state. I have tried for a few seconds to think about this, and immediately after that I felt a panic attack. Which I'd very strange to be honest, and I don't understand why this thing happens. I have tried multiple times this exercise, but the result it's still the same. Why is this thing occurring in my case ? 
My anxiety started once I smoked some weed with my friends. Before this, I never had a problem with it. Nor do I think it is related to a traumatic event