Panic attacks aren't always about anxiety one can identify as such. One's body chemistry, medicines one take, etc. can cause panic attacks. Panic attacks aren't always cause and effect straight, can be more complicated like stress headaches (a lot of people can't identify any particular stress) or other physical reactions of that nature.

It sounds like you need to go see your doctor, have some tests, tell him what is going on with your sleep and other reactions. It can be hard, if your body gets in the "habit" of panic attacks, to work with them and often, addressing them right away and ruling out other possibilities can help lessen your mind's and body's reactions in the future.