Scubadam
Contributor
It could be several things. Some ideas I have include to fast of a descent, diving to deep causing decompression sickness, during a descent if you do not give yourself enough time to equalize this could lead to having a light head. Another reason maybe that you are acending to quickly, or ascending without a safety stop depending on how deep your Max. depth is. But I would go to see my doctor if I were you because this problem may not be from diving alone or at all.