Anxiety can present without any of the more common symptoms. What you're describing is more of a "total body" anxiety...........but it's still anxiety. And like most anxiety/panic, it does just come "out of the blue." Which is most likely why we call them anxiety "attacks." I would urge you to discuss this with your doctor as sometimes there is an underlying physical cause for these sensations. You need to have those ruled out before a definitive diagnosis of anxiety disorder can be reached.
I wish you the best.
GAD, if you have it, and you really don't as it's present all the time, not just once in awhile, can be caused by negative thoughts that you don't notice until you learn about them in therapy. As for your "vitals," that isn't how you check for a physiological cause of anxiety, and you won't get a thorough check-up by calling 911. You have to see a regular doc for that, not someone doing triage. Many things can be causing this, including blood sugar imbalances, hormone imbalances including thyroid and testosterone and other sexual hormones, hidden viruses, nutritional deficiencies, etc. This stuff can be very hard to find, and most docs won't look very hard for them. But it's still important to get a really thorough check-up anyway. If it isn't physiological in nature, it's anxiety, and as Ruby said, for most of us it just seemed to come on out of the blue. "It" doesn't require you to stop what you're doing, you choose to do that -- it's called avoidance, and it's what turns us into chronic sufferers. When it gets to that point you need to do something about it before it gets way out of control. Good luck.