Can you develop anxiety all of the sudden and what can cause this?

Just recently I have been experiencing a lot of anxiety symptoms, (feeling like life is a dream/ drifting in and out, feeling like I have brain cancer and I'm going to die prematurely, loss of appetite, waking up scared, panic attacks, increased heart rate, feeling like I'm going crazy, that sort of thing). The past few months have taken a major toll on my personality- I had a near death experience, I just wrote 4 diplomas that I'm unsure of, and my friend ped away. I've been a perfectly normal 18 year old boy up until these recent events and now I'm completely different. I think I've developed anxiety but I don't know if you can develop it this late or if it's hereditary. Tell me some of your experiences if they relate to mine and you have anxiety problems like me.