It's quite common, basically the energy build up goes to your head. It's nothing to worry about and typically goes away fairly quickly however if it doesn't then you may consider grounding yourself after the spell/meditation to help reset your energy.
By: Lark Moderator / Knowledgeable Feb 16, 2013
Post # 4
Most likely because you aren't grounding and centering properly before and after doing spell work. As a result you are draining your own energy and leaving yourself open to dizziness, headaches, and other problems.