The blacking out that you described is also known as syncope. You say "to the point" so I understand that you "almost" black out, but not quite, which would be called near-syncope or threatened-syncope.
This is caused by insufficient blood flow to the brain. More specifically, it is when the brain does not recieve enough oxygen. When the brain doesn't get enough oxygen, it is thrown into a sort of panic mode and it shuts down, causing you to lose conciousness, or in your case to feel dizzy. This is your brain's way of saying "hold on, I need some air!"
The most likely cause for this is the manner in which you are laughing. You are probably laughing in a way that you are not breathing adequately. This may be due to "silent laughing" where you are actually holding your breath, or you may be breathing too shallowly and rapidly for adequate oxygen exchange to occur in your lungs.
The best thing to do is to be aware of this as a problem. Next time you laugh, practice being aware of how you are breathing. You may need to force yourself to take a few slow deep breaths. This may be difficult because the manner in which you laugh is a deep-seeded habitual behavior. However, if you are aware of your need to breath and you can begin practicing slower, more effective breathing, this will eventually become your new habit and laughing will be more enjoyable.