Anxiety can definitely play a huge factor. I was diagnosed with an anxiety disorder a few years ago, and I have conquered it for the most part (severe stresses can get me going, but I am much less a worrier than I used to be). Here is what I recommend:
1. See a doctor or therapist. Seriously. I actually went through testing because I had several symptoms that could have been either anxiety or ADHD. I scored off the charts for ADHD, but those symptoms were largely caused by anxiety (especially the inability to concentrate). They put me on a beta blocker and it helped amazingly. It also helped control my pulse, which would get erratic from stress, caffeine, etc.
2. Go for herbal supplements. I had previously been taking valerian, a natual herb, to help me sleep because my brain would be so active at night. Then I noticed it's also useful for daytime anxiety. It does not cause drowsiness at all; it just quiets the brain's nervous energy so you can focus better and relax a bit. You can get it as a tincture that you drop on your tongue, or a capsule, which is what I use. It's a stinky herb, so I get mine from a company called To Your Health because theirs is virtually odorless compared to the ones I've found locally (www.e-tyh.com
3. Change your diet. I stopped taking the beta blocker after a while (my hair was thinning and they can affect that, so I decided to stop taking it), but my rapid heartbeat and general edginess returned. Then I learned I was hypoglycemic, and I stopped eating sugar and starchy carbs, and not only did my heartbeat stabilize and calm down (I now have a lower resting heartrate), but virtually ALL of my anxiety symptoms disappeared!!! I was stunned. Even asthma symptoms disappeared. When my heartbeat was rapid, it made me feel anxious. I will on rare occasions eat refined sugar, but I limit myself as much as possible (you do get used to it after a while and a lot of products are made with Splenda, a great sweetener). I wouldn't do any drastic changes to your diet without talking to a doctor, but cutting sugar out of my diet has completely changed my life and my health. I don't take any medications for anxiety at all, and only rarely have an anxious episode when something really heinous happens and the stress was already building.
I hope this helps!!