Joyce47oh, Make sure that your mask fits correctly, sometimes after weight loss/gain the mask needs to be adjusted. Also tell your doctor about the problem, he may suggest increasing the setting, it may not be high enough to keep your airway open through the night, thus interupting your ability to enter REM sleep leaving you tired in the A.M.
P.S. Yes sleep apnea is a serious condition when you stop breathing from the obstruction at night your brain is unable to recieve fresh oxygen and so is the rest of the body. Energy levels go down , memory is a problem, etc. so keep up with your doctor for the best treatment for you.