Breathlessness, Increased Heartbeat. Have Atrial Septal Defect

Occasionally when I m going to sleep, I get this horrible feeling like I m dying or something, and i realised that I ve actually stopped breathing . The time were I m not breathing only lasts about 5 seconds usually, but it has gotten up to about 30 seconds before. So about five seconds after I ve stopped breathing, I gasp in a big and quick breath through my nose and then there is only about a 4 second gap until I stop breathing again and the problem continues. Usually this happens while I am still kind of awake and just getting to sleep, about 5-10 minutes after i lay down, and I can t sleep when this happens to me because it s disturbing me every time i am almost asleep. This has happened to me in the middle of my sleep as well, and that time was much more scary, I could feel some how in my sleep that I wasn t breathing and after about 30-40 seconds I immediately sat upright and took a really deep gasp, and my heart was beating so fast. I usually get tired during the day and I always fall asleep on the school bus and sometimes take naps at home, I sleep at about 11pm and wake up at 7am. I m 15 and i weigh 46kg and my height is 159 cm. I do have a couple of health conditions such as an ASD ( Atrial septal defect ), sinus mucosal disease(but it s quite mild) and I was born with gastroesophageal reflux disease , but the stitches of the nissen fundoplication operation have come undone. I m just sceptical about weather this is sleep apnea because i don t snore and it happens a lot in periods of time and only occasionally, definitely not every night.