Your prisoners’ stats when you open your game will be directly affected by your staff hired before you had left the game. You would need to adjust your growth strategy accordingly. If your prisoners have health rates very low when you go back into the game, make sure that you hire more doctors or upgrade food servings, for example. 
Take in mind your special prisoners (tap on the prisoners’ button, lower-right corner icons on your playing screen, and then tap on the red skull button to know more about them). They could directly affect your prisoners’ mood!