Anxiety Support Group
Anxiety is a physical condition marked by intense and persistent feelings of distress, fear, angst or dread. General anxiety caused by routine day-to-day stresses usually passes quickly and is experienced by almost everyone at one time or another. However, such feelings that linger over time and are very difficult to cope with, and which lack a clear cause, may indicate...

You can often have just one part of the body displaying overload tension, and when it goes into overwhelming tension, you have missed the little signals along the way.
Hope this helps.
Thanks for all your advice. I feel silly posting that "I don't know how to tell when i'm upset." but I really don't.... I was feeling really bad last week, fatigued, weak, no energy... and I think it was anxiety.