People have all sorts of reactions to smoking weed, inlcuding fainting and dizziness, jitters and perspiration and agitation. Depends on the individual who's smoking, how he's feeling, and how the weed affects him. I'm sure it also depends a lot on the strain you're smoking and what its sativa vs indica content is.

Consider your response easily within the realm of normal from what I've read about responses to weed, albeit a strong enough response that it'd be wise to proceed cautiously the next time. You may find some interesting and reassuring info on one or both of these sites:
http://www.erowid.org/ (see Plants & Drugs/Cannabis)
http://www.norml.org/ (navigate to the Medical Use area)