Welcome to the board. The dizziness you are feeling can be attributed to a number of things.

One of which could be if the cigar is “green” (when the cigar isn’t aged by the manufacturer or isn't aged long enough). Some companies rush their cigars on the market and don’t age the cigars for a period of time (which can leave higher amounts of nicotine and other chemicals in the cigar). If this is the culprit you could let the cigar sit in a humidor for a couple of weeks or months (over time the levels of nicotine, ammonia and such will level off and won’t be as harsh).

Another culprit could be the body of the cigar. If you just started smoking, full body cigars may be able to give you this feeling, especially if your smoking on an empty stomach. (I would recommend you eat a meal before you smoke a full body cigar, especially if you just started to smoke).