Back story:
I spent 4/5 nights in hospital after DC was born.
I had DC late at night. Woke up at 7.30am in a fright because I thought he was dead. He was not. Just sound asleep.
I enquired to the Midwife on duty and she said she knew, she kept checking on us both but we were just sleeping.
I thought no problem, one off from birth but 2nd night would be normal 'newborn' experience. Wrong. DC slept from 10pm to 7.30am again. But this time I was awake constantly because of other babies on the ward crying! Same thing happened until we left hospital.
Ironically, the other thing keeping me up at night was other people's babies 
I kept expressing my concerns of him maybe getting dehydrated during the night and the midwives insisted I didn't wake him. So I didn't and enjoyed my sleep well what I could get of it since other people's babies just wouldn't shut up
Before we were discharged, I spoke to the paediatrics Dr. Again, reassured to count my lucky stars and not to wake him.
So I didn't. Went home and just let him sleep through consistently, night after night.
Fast forward to 5 weeks old and he put himself into a routine of 9pm to 9am, so 12 hour slots.
Fast forward to now at 4.5 months. Still the same but often doesn't wake until 11am.
I'm getting worried because usually I just let him wake himself and he's a happy bunny. But recently I've been trying out a few local things and he's so grumpy. For example, stay and play starts at 9.30am. He doesn't take kindly to being put in a pram and hoisted off.
I didn't know what to do in those early weeks because all the baby books and stories prepared me for sleep deprivation, not over sleeping!
It wasn't until a friend of mine commented that when her premature baby was born, she was told very clearly not to let them go over 4/5 hours because they could dehydrate or be jaundice. She said she thinks what I done was dangerous and the medical professionals advising me to let him sleep should be questioned.
Furthermore, I saw a someone with a similar baby post once and people kept saying letting small babies sleep through is indeed dangerous and to wake them.
AIBU to ask for bloods? I'm scared he's too sleepy/lethargic. He's an older baby now and still the same. I'm worried there may be an issue, of some sort.
Otherwise, he's a very healthy and happy baby who just gets very cross if things are too loud and he's trying to sleep.
He's also gained weight very well and put on instead of lost in his first week of life outside the womb.
I don't want to waste NHS time but at the same time, I don't want to miss anything abnormal. What if he has an illness I don't know about?
Obviously I'm not going to wake him now because he's an older baby. But could his overall sleeping habits be a sign of something?
It can't be normal because it was bashed and hammered home to me so much during pregnancy that I would Be sleep deprived, not setting alarms so I don't over sleep and end up getting myself ready and gone 12 in the afternoon by the time I've had 'breakfast' and given DC their first feed 