Hello and thank you for your query
The allergic reaction
could be due to some kind of viral infection or it could be due to some kind of allergy
to an allergen in new surroundings (ie hospital).
Wait for a day or a two and watch for the allergy. If it does not resolve in 1-2 days then you should consult your family physician to know the exact cause of the reaction.
Hope my answer is of help to yopu.
Do send me a follow up mail.