GP is your first call, agree with those who have suggested this.
You should never feel alone when going through something like this and the simple act of talking about it to a medical professional may ease the feelings.
Your GP will investigate as to the cause, physical or psychological and then work a solution out with you.
Many of us get like this, I know I did. I went for a course of CBT (cognitive behavioural therapy) to ease my anxiety. It isnt like counselling exactly, but it teaches you methods to ease the stress you are feeling towards every day situations.
The impending doom thing is commonly related to stress and anxiety. You say you have no obvious truobles but often its the "non obvious" things that build up in our minds.
Good luck