I think if you were very ill it would be normal to not necessarily remember it.
Although I had pneumonia very badly aged 3yo. Dm said she wasn't sure I would survive the drive into hospital (and I wonder why they didn't call an ambulance from the centre 10 minutes away rather than choosing to drive me 40 minutes at best to the hospital through rush hour traffic
)
I remember it clearly. I remember asking to take my seat belt off so I could lie down because I was tired, and being really surprised when dm said "yes" as she was really strict about seatbelts. I talked about that a few years ago, which was when dm said they didn't think I'd survive the journey anyway.
I remember sitting on the high bed with them trying to persuade me to take the medicine. I refused, arms folded, shaking head. So they injected me. I felt that was cheating.
I remember the day they cleaned the ward, and the huge hoovers they used. And the fire alarm.
I remember deciding I would scream blue murder when it was time for dm to go in the evening so she'd be last to go. I also remember the feeling of relief when the door closed and I could just go to sleep without trying to keep her there any longer. 
I remember taking medicine and vomiting it straight back up, and thinking "your fault for making me take it".
I remember them tipping the bed down to try and make me cough it up.
I remember the boy next to me. I gave him some biscuits that I had. Pity he was in for tonsil removal, and he had a sign saying "nil by mouth". 3yos can't read that. Oops.
I remember the boy who wouldn't stay in his cot, so they put him in with a lid on it.
I remember the little one who threw the jug of water from the bedside cabinet at the nurse to was trying (fairly nicely) to quieten her down.
That's just a selection. But, you know, I have absolutely no recollection of feeling ill at all. If I had been kept at home I doubt I would realise that was the time I'd been so ill. I can date it to then as I was in hospital and that was the only time.
It may be you do have some recollections from that time, but you're not associating them with that as there is nothing that marks it out to be that specific time.
Memory is a strange thing.