My baby is having strange spells at night...?

For the past 1 1/2 months my now 5 month old baby has been having episodes at night of waking up screaming (not crying, but shrill screams!). When I get to the nursery within a few seconds his tongue appears greyish-blue and when I pick him up he is completely limp from head to toe. He continues to cry hysterically for about 5 minutes and is unable to hold his head up and will not open his eyes. Then it's like he snaps out of it and opens his eyes and holds his head up and is fine. He will go back to sleep and not wake up until morning, just as he normally does. It always happens 1-2 hours after putting him to bed and it always happens when he's sleeping in his crib, never anywhere else. It has happened 5 times now, and it usually occurs 1-2 weeks apart. What on earth could this be?! I have looked everywhere! His doctor thinks he has severe GERD and I really thought that he was just getting a little choked on formula (causing the tongue to look a little greyish) and scaring him