Heart rate rises when exercising then falls dangerously slow.

[ptgarner]

Heart rate rises first 4 or 5 minutes of riding a stationary bike and then begins to fall....resting heart rate about 80....rises to 110 at first and then falls quickly to low 40's....strangely enough I dont feel out of breath and dont feel at all out of breath..(.in fact if I hold my breath for 30 seconds,  I feel no distress but it makes my heart rate plummet..)..if maintained it will drop in the mid upper 30's and I start to feel nausiated  and about to throw up...
   Once I stop exercising, it will rocked back up to the 90's within 1 minute....
What in the world could cause this??

Age 62....overweight with high blood pressure...150/103...sleep apnea but trying to loose weight and get back in shape...