Since this feeling began suddenly a month ago and is causing you some anxiety, I strongly suggest you see your doctor. It could be your thyroid, adrenal glands, or a number of other things, but it does need to be evaluated.
Too much adrenalin can cause fear because it is the "fight or flight" hormone that is released when we're facing danger. When it gets released when there is no danger, it can be very frightening. For those of us with anxiety or panic attacks, adrenalin is NOT our friend as it affects nearly every major system in our body.
I can pretty much promise you that this isn't happening because you sometimes have too much time on your hands.
See your doctor, who will run some blood tests and probably have an answer for you in a day or two. Be sure and mention the anxious feelings you get, but don't let that stop your doctor from running tests! Insist on the tests. Too many doctors will simply put your feelings down to anxiety, especially in women, and it may be years before we are accurately diagnosed.
I'm sure it's nothing serious. Let us know what you find out, OK?
I am getting these rushes more frequently and I know it is because I have some heart arrhythmia problems from time to time which I can clearly hear because of tinnitus and which cause me anxiety by day and sleeplessness during those nights, and the adrenaline can precipitate these attacks or keeps them going, so it is vital I must keep them at bay.
So far I have resorted to deep breathing at the onset or even holding my breath for periods (sometimes works) - does anyone know of any other tricks which might help?