J Griff,
I think you are having a panic/acute anxiety episode.
Have you had a panic attack before?
Did you eat this morning? Caffeine can be a trigger, especially on an empty stomach!
Try drinking some water, having a snack (high protein/complex carb, not sugary!)
...and try this self help exercise.
http://www.ehow.com/video_4405003_breathing-exercises-panic-attacks.html
Let us know how you feel afterward, okay?
S.C.