I collapsed and stopped breathing. went to the hospital and they did test on my heart and determined it is fine. what elsecould have caused this?

Many: You could have had sudden apnea, or vasovagal or arrhythmia or metabolic derrangements. More information is needed. Discuss with your primary physician.

Several ideas: Was a pulmonary thromboembolus ruled out? Will you be getting a holter monitor for possible heart block / other need for a pacemaker. This needs to be run over a few days. Is this a seizure or syncope? The differential diagnosis is a long one and the entities to be considered will depend on what surrounded the event. Hoping a treatable cause is found. Thanks for writing.