Is this a bee or a fly?

It appears to be a bee, we have similar looking bees here in Chiang Mai. They are quite often attracted to lights at night. While they can sting they are not aggressive, and will fly away in the morning if they can get out.

Adam.

PS. I see that you said you got "bitten" by one recently, you did not state that in the post on the other forum, and I just copied my answer there above here. It will actually have stung you with the end of its abdomen rather than bitten you with its mouth. Bees have barbed stings, and often the long term allergic reaction is more a result of the sting tip breaking off inside the skin puncture rather than the actual poison itself. If you didn't already do so, you should ensure that the whole of the sting has been removed. If the allergy persists you should go to see a doctor.

It is worth noting that wasps do not have barbs on their stings, so any reaction to a wasp sting is purely a result of the poison injected at the time. There is an old saying that is very helpful if you treat the sting immediately "Bicarbonate for Bees and Vinegar for Vasps" - this means you should put bicarbonate of soda on a bee sting but vinegar on a wasp sting. The reason is that the alkaline bicarbonate counters the acidic bee sting, but for wasps you need vinegar (acid) to neutralise the alkaline sting.