would there be a better, more medival or renaissance-like word to describe a sleep aid? Or if not, to describe medicine in general? Thanks,

I would think you could use terms like remedy or elixir. You may want to google alchemy for some ideas.

Thanks!

'sleeping potion' used to be a popular term for 'sleep-aid'...

there were doctors in the middle ages, but medicine in general was often handled by 'chemists' or, in rural areas, by a midwife or a local 'healer' of one sort or another...

I imagine alcoholic beverages were popular sleep aids as well.

a term also widely used is/was 'sleeping draught'...