At the end of the day, the OP can do what she wants. The chances are that nothing very had will happen, but there are enough reports on here AND in real life of small children getting into dangerous situations, that there is a genuine risk.
We all have to live with risk and yes, it is possible for a small child to do something daft doing the 2 minutes we are in the loo - we have to minimise the risk by not leaving dangerous stuff around, but we cannot totally remove the risk.
The question is about what is acceptable for different age groups. Again, there are grey areas, but I maintain that there is a difference between an adult being present in the building and alert to the fact something might happen which requires them to come quickly (the situation when the parent is just in another room for a while) and being in what could well be a deep sleep (more likely if hungover) so NOT alert to possible issues which could arise. This is why so many people have advocated a little doze on the sofa as preferable.
I think the situation would be different if the children were older - again there will be grey areas and some people will be happy to leave their children downstairs whilst sleeping at different ages.
I suffer from awful migraines. I dreaded having one when I had toddlers. If i did, I lay on the sofa downstairs with them and just had to wait for it to pass. It was truly awful, but I was there and could respond if something happened. Once they were older, I would go upstairs, because a 5 year old with an 8 year old is quite different from a 3 year old.
I always wonder why people post on AIBU when they are not prepared to even consider that they might be - is it because they want a fight? Is it because they are unable to acknowledge value in what someone else says, because it seems like 'backing down', is it that they really do realise they might have been wrong, but cannot bring themselves to say it. I just find the whole thing odd.