There are legal differences between sick leave and vacation, at least where I live. The former is required by state law, the latter isnt. Vacation hours can be

There are legal differences between sick leave and vacation, at least where I live. The former is required by state law, the latter isnt. Vacation hours can be accrued and have a cash-out value, sick leave will expire. There are a bunch of other rules as well. You should never have to reveal the nature of any health conditions to an employer to take sick leave.