Health in KCD2 doesn't generate automatically and you need to eat some specific foods or sleep to get it back.

Sleep

Best and easiest way of restoring your health is to sleep.

1. Go to any town or small village and find a house with bed in it.

2. Choose Sleep option next to bed and set the clock.

• The more you sleep the more health you regenerate.
• Don't sleep on beds with angry owners, they will wake you up and attack you.
• If no one is letting you sleep in their house, you can always go out and find a single house in the wild, kill the owner, loot him, and take a rest in his bedroom.
• It might be hard (or easy if you are lucky) to find one, but you can sleep in camps in the wild too. No angry owner, no cost or anything else to bother you.