What Causes Short Pauses In Breathing While Sleeping In A Premature Baby?

Question: Hi, 6 months ago i had a baby born at 37 weeks 2 days gestation who sustained severe head trauma related to a traumatic birth. He was diagnosed with HIE (however i do believe it was the least severe grade as developmentally he is right on track, Thank God!!) he sustained two skull fractures, subdural bleed (no midline shift) and petechia bleeds in his ventricles (which was only seen on his day 8 MRI which otherwise was pretty normal). He has had multiple eeg's and although his most recent (at 3 months old) was abnormal showing bi temporal sharp waves he has never had any seizure activity (again thanks to his amazing medical team and thank God) and so was weaned off his phenobarb. He does have gerd and is currently treated with losec for the same, no issues with nursing or weight gain.
My question to you is this- up until he was 4 months old he slept really well, waking 1-2/night. However since then he wakes quite frequently as much as every hour. Given the extent of his injuries i am wondering if sleep apnea could be an issue and whether it would rear its ugly head this late in the game. He doesnt snore but does some times have a big XXXXXXX or small gasp while sleeping (its not a gasp like coming up for air it sounds more like his little laugh he does in his sleep however hes not laughing because there are no smiles and its only one quick noise, when hes laughing in his sleep its an audible laugh). His lips and nail beds are always pink, however occasionally he does have short pauses in his breathing (which i know is also normal for young babies- its never been more or even up to 20 seconds that i know of). In nicu he was obviously continuously monitored and apnea was never an issue there but with these new sleep issues despite sleep training methods i just want to make sure im not missing something more significant. Your thoughts would be appreciated.
Thanks