Were their any equivalent of medics in medieval warfare or did soldiers just get patched up by fellow soldiers? Similarly, do maesters go to war with their lords? Seems like even the great lords only really have one maester per castle, so would they need another one to stay behind while they’re at war? We’ve seen a few examples of maesters on the field, but where are these guys coming from?

Well, historically there were healers for the nobility, but the common soldier made do. Keep in mind, medicine was extremely crude in the medieval era (including some important steps backward from the Roman era when it came to antiseptics and surgery), so there wasn’t much you could do besides stitch people up, use maggots and/or cauterization, and hope they don’t die of an infection. If you were very lucky, someone might use a herbal poultice that used the right kind of bread mold, but chances aren’t great.