Yes, apnea is a sleep disorder which occurs when a person’s breathing stops or get interrupted during sleeping. Lack of oxygen in blood and body's inability to store enough oxygen leads to apnea. When brain and body do not get oxygen, it makes apnea condition worst, and one may find it difficult to breathe while sleeping. Anyone suffering from apnea should consider visiting a doctor before traveling to any higher altitudes, as it may cause severe health issues.  Source: (https://www.sleepapnea.org/)