
It's worth noting that the fortify action doesn't work with mounted and armored units as stated. Being completely healed is useful against ranged units who can get a bonus against injured units. Providing that the units need to not do anything in order to heal, they could fortify while waiting as well, so this action is very handy.

Naval units cannot heal outside friendly tiles. (Like having Iron: -1, this prevents sword and artillery units from healing and they get a penalty to attack). If the unit requires a strategic resource from which the player may have run out then the unit does not heal.

When a unit doesn't move and is injured, it heals:

A very common reported bug is that this or that unit is not healing as intended, let's hope this clarifies.
