What Causes Oxygen Level Issues Related To Sleep Apnea?

Have been diagnosed for oxygen levels related to sleep apenia. Negative. Have mild blood pressure issues. Taking medication. At night wake up after dreams of excursion, sometime 3-4 times a night. Heart beat not out of control, but beating harder, but not out of breath. Calm down after 15 minutes. Exercise regularly, not out of shape for 73. Work 3-5 hours a day on yachts. 1/2 hour nap a day. 6'0" 195. Thanks, Rick