This power-up is found usually when a large battle is following. Thus, they should be used sparingly. They can be found in secrets that are normally hard to access or a suicidal trap.
In Serious Sam: Xbox and Serious Sam: Next Encounter, if you're playing on higher difficulties, be aware that if you grab it when you have 100 health, your health will start decreasing by 1 HP per second. Thus, strategy is required before grabbing Super Health.
Super Health has appeared in all Serious Sam games. It always gives the player 100 health points when picked up. They are usually found in secret areas, such as in Tomb of Ramses III, which holds 2 of them, both of which are secrets. Otherwise, they mostly trigger traps, such as a lot of Kleer Skeletons rushing at you. There will always be a reason for the game to give you one, or the game just tries to be nice and give you some health.