I've never had a panic attack, and I'm not depressed, but I don't talk to people more than necessary, I've never made an offline friend/relationship and any feeling that someone ahead might say hi to me or something makes me anxious. So I think you can have severe anxiety issues without panic attacks.
Think of it this way: some people may seem normal while their anxiety builds up in the background to explode in a panic attack, while other people's anxiety is a more even, constant thing. You can have a brief downpour or a steady light rain and get the same amount of precipitation.
Since you believe your anxiety stems from grades and body image, though, that could go against definitions of social anxiety which require that the sufferer be aware that their fear is irrational. (It'd be a different anxiety disorder, in that case.)
"Laughter and tears are both responses to frustration and exhaustion. I myself prefer to laugh, since there is less cleaning up to do afterward."
- Kurt Vonnegut