*squishes* I know the feeling hun, I know you said nothing was going on, but were you thinking of anything?
Under any stresses? Like exams coming up or coursework due in? 'Cause that sometimes causes mine...like subconciously...
Y'know holland+barratts? well they sell a 'rescue remedy' spray, it helps with panic attacks, I have it. If you keep getting them maybe you could give that a try? sorry If I'm not alout to advise things like this but it's completely natural medicine

*hugs*