Or check them to be doctors... they eat and drink regularly on their own.. just take them to the cactus and make sure they get the first notch of training.. after that, they'll take things easy and get back their health
It always seems way longer to get a weakened villager back to full health, so check their health bars and if they go down 2 or 3 notches, take them to the bin a few times, till it jumps back up at least a notch.. then you can get them back to research/building faster.