It could have been a build up of energy. After performing magick, do a grounding exercise and have something to eat. You can do a search on grounding using the site tool bar, there's plenty in the forums :)
I totally agree with Zebrah. After a spell, relax, forget about it, do a short relaxation meditation exercise.., for example think of a beach scene in your mind where you are sitting in a beach chaise lounge chair and you see the ocean blue with calming waves undulating coming and retreating on the beach shore. Think of the beach sounds, the soothing wave sounds, the sound of a calm sea breeze, the sound of sea gulls prancing in the air. Totally engulf your mind with a calming scene like this, with no excitement like a radio or drinking a beer or mixed drink with a small parasol on top. Just RELAX! After just 2 or 3 minutes, let it go. Do something else.
I hope this helps. A fellow student.