Lots of valid comments here, but your body creates it over time. Until you're 100%, you are more susceptible to infection, crave an iron-rich diet, and become

Lots of valid comments here, but your body creates it over time. Until you're 100%, you are more susceptible to infection, crave an iron-rich diet, and become tired more quickly. After a while you just realize you're back to normal and forgot you ever felt weird. For me it took 14 days before I had full energy, and 30 days before I quit getting tired easily.