I wont know if I cease to exist so there's no point worrying.
I just felt completely overwhelmed by a sudden wave of existential angst.
for my experience existential crisis is fatal situation. you need to see an expert, a doc. problem is that it comes as and effect of too many things working on background.
in simple you are infected of some nasty psychological issues. it will come as you start enjoying your problem and embrace it more in to you. its danger, you need a break. go and see and psychiatrist (not a psychologist!). you may show severe symptoms of several combinations of bipolar disorders. its much more complicated than actually it seems. the first and major difficulty you face is to convince yourself that you have some problems and you need some treatment. make your decision as fast as you can cos next level of the disorder may not the that sweet! find a good doc around you and tell him the facts in its right degree cos if he got misunderstand you may get in to more troubles. new psychiatric treatment are using Atypical anti-psychotic drugs.
stop booze and smoke for some time. strictly no grass or other drugs. you may experience slight sexual dysfunction problems. don't worry everything will return back to normal as you get queried. do some exercise, its not for your body its for the mind. make routine for food, sleep and work. eat and drink. you will surely get queried. :)