At the start of the game, Jason has two blocks of health. If a given injury depletes part of a block of life, it gradually refills itself if you can go for a few seconds without taking any more damage. You can eventually acquire up to four additional blocks of health by purchasing the appropriate skills.
Once a block of life has been emptied, it stays that way until you heal it. You can purchase Medical syringes from vendors for $100 apiece, find them in the game world inside white and red medkits, or produce them yourself through crafting, for the cost of one Green Leaf per syringe. They heal a base of two blocks of life each, and can be augmented to heal up to six by acquiring certain skills. You receive the Needle Exchange Achievement/Trophy for creating a total of 25 syringes, and Medical syringes are likely to be a significant portion of that number.
If you have no Medical syringes on hand, you can also employ basic first aid to restore some of your life. This takes a second longer than using a syringe and isn’t quite as effective, although like syringes, you can purchase particular skills to improve the efficiency of first aid. These skills may seem like a waste of points, given how common medkits and Green Leaves happen to be, but they’re useful in certain story missions towards the end of the game.
Green Leaves are very common in the game world, although they are not native to every part of Rook Island. They’re particularly rare on the South Island, so it’s useful to stock up on them whenever they’re readily available. The countryside around Amanaki Village is particularly full of them.
It is very easy to take more damage than you think you did in Far Cry 3 . Jason can absorb a couple of bullets without it really slowing him down, but sustained weapons fire from multiple targets, melee attacks, certain animals’ bites or claws, explosions, and fire can all drain your life very quickly. Even if you think you’re in good shape, stay moving, make use of hard cover, and keep one eye on your health meter. Syringes are cheap, and you should never hesitate to use one even if it seems like a waste. You are always closer to dead than you think you are.
This goes double for falling damage, which ramps up quickly. Even a short fall can knock off a block of Jason’s health, and anything higher than forty feet or so can kill him outright. (Jason is heavily bullet resistant, but as you’ll discover over the course of the game, he’s got bad knees and a glass jaw.) Be very careful around high ledges.
In the event that you die, you return to the closest safe house or equivalent location. Your equipment and accomplishments are reset to what they were at the time of your last auto-save, and any random encounters you ran into have since reset and despawned. You are not able to die your way through an encounter in this game.