4 year old Vomiting once at night, for 4 nights?

[newbabyinthestow]

For 4 nights now my son has been sick, just once per night, in the middle of the night after going to bed normally. He wakes up fine in the morning and first day it was the weekend so just told him to take it easy, but last two days he has woken up full on beans, asking for weetabix and has actually asked to go to nursery. He seemed so fine and is eating normally, I keep thinking its over, and he has been fine each day during the day, but was sick again tonight....what is going on?? He is 4 years old. My brother who lives with us had a violent vomiting bug over the weekend, but my son was ill before that...is this just his weird version of the bug? Is it a different bug? Is it something else and my brother's 48 hour sickness is just a coincidence? I am stumped....

Had he ate before bed? I read once (but of course I can't bloody find it now) that sometimes children are sick if their blood sugar drops from not eating for long periods of time.

Acid reflux is also a possibility.

Could just be a bug though, their is some very weird stuff going around.