Thank you for your querying.
It is not common for a child to faint after nose bleed. But it may not always be serious. As you said he was scared. That may cause a nervous shock
on seeing so much blood and fainting
. Blood glucose
is usually maintained at a static level in a normal person unless one starves for a very long period. So you are right in thinking that low blood glucose may cause fainting but it is unlikely that your son had low glucose if he had taken lunch and dinner. Thirdly loss of lots of blood suddenly can cause transient low blood pressure and resultant fainting. Lastly what we are most scared of is a bleed inside his skull or brain which may cause fainting. So ideally if there is any loss of consciousness
we tend to get a CT scan
done. But since your son has done well for 2 -3 days since then you may skip the CT as he is not likely to have it. So whatever caused the fainting should now be taken care of and you need not worry. Hope this solves your query. For any further queries, contact a pediatric surgeon.
God bless you