each of your questions is possible
yes the hospital could have given him sedatives depending on the doctor some will prescribe sedatives some wont he also had a saline I.V in at the very least saline can cause a seizure under the right circumstances (maybe not 2 days later however)
he could have faked it
it isnt difficult to fake a seizure and he could have faked them in the past for attention
there could be a medical reason why he had a seizure
many medical issues can cause seizures