o2 desaturation

For the past several years, I have had many episodes (that happen maybe 3 to 20 times per month) where I get suddenly dizzy, confused and racing pulse....it never last long, I feel normal again after 20 seconds and my pulse slows back down within the minute.      I was wearing a medical grade pulse oximeter and I am certain the reading was right, it dropped suddenly to 81 a split second before one of these episodes and went back to the high 90's after I felt normal again...I know it was right because it correlated so directly with my symptoms.  

What possible explanations are there for this, in a 33 year old man?

[Darcy Green Conaway, MD]

Your symptoms sound consistent with an abnormal rhythm of the heart. These usually don't cause low oxygen levels but it is possible. I would recommend a heart  monitor that you wear to evaluate your rhythms; I would also suggest an echocardiogram to make sure there is no shunt (hole in the heart that allows blood to cross where it shouldn't)