Almost every night, rick's roommate appears to stop breathing while he sleeps. rick mentioned this to his roommate, who then went to the student health center for a consultation. it was determined that the symptoms of rick's roommate were caused by

Sleep apnea

Explanation:

Sleep apnea is a sleep disorder where a person pauses during breathing or breathes shallow while sleeping. Each pause may last for few seconds to few minutes and it can occur several times in one night. It is usually preceded by a loud snoring. It ends with a choking or snorting sound after which normal breathing resumes. It disrupts normal sleep and the person might feel tired the next day.

Sleep apnea maybe obstructive which means that the breathing is hindered by a blockage of air flow or it might be central in which unconscious breathing simply stops or it might be a combination of both.

Since Rick's roommate stopped breathing several times while sleeping his symptoms were most probably caused by sleep apnea.