The section on Dying states that:

All damage that you suffer lowers your Health, and when your Health drops to zero or below, you immediately fall unconscious. The next attack that hits you will kill you.

The section on Medicine states:

The Target Number to heal a character is always 15. With success, the character regains 1 Health, plus the amount by which you beat the TN.

Example: If your result (ranks + dice roll) equals 19, then the patient regains 5 Health (19 - 15 = 4; 1 Health + 4 = 5 Health)

You can also use Medicine to save a dying character. The TN for this check is 20. If you can reach a character within one round of them dying — that is, within one round of them taking a hit after they fall unconscious — you can make a Medicine check to save their life. With success, you revive the character with a single point of their Health remaining...