After one month of CPAP use men with severe obstructive sleep apnea (OSA) suffering from erectile dysfunction may see improvement even remission. The cause of impotence in the first place is likely related chronic sleep disruption due to hypoxia from airway collapses which leads to a hormonal imbalance. Testosterone is actually secreted during a deep stage of sleep right before entry into REM sleep. Those with untreated severe obstructive sleep apnea often have significantly (sometimes absent) deep sleep and REM sleep. Thus, low testosterone levels with consequent loss of libido and erectile dysfunction are common.
The good news, treat the OSA and get your mojo back!
Erectile dysfunction, obstructive sleep apnea synd... [Sleep Med. 2005] - PubMed - NCBI
Here are some other health effects of untreated sleep apnea: