I Am 60, Fairly Fit, Have Low Heart Rate And

I am 60, fairly fit, have low heart rate and very good lung capacity for my age, but I've noticed that my breathing slows and becomes very shallow when I'm sleeping to the point that it stops and then eventually there is a panic reaction and I wake only to go back to sleep and start the process again. It isn't the same as sleep aphenea (forgive the spelling) there is no snoring or blockage just a gradual loss of function. I find it quite frightening.