sick days are not planned for. Vacation days have to be planned for and organised in advance.

They are separate. Vacation days must be approved in advance. (find out what your company policy is, but at most places you have to book these days at the beginning of the year in January). Sick days are days in which you do not show up to work because you are sick and are not planned in advance. Some companies will do investigation work to make sure you actually are sick. So don’t lie about it. Besides, if you ever wanted to use someone at that company as a job reference in the future, imagine how great it would sound when they say “so and so was never absent.”
Good luck! And talk to your HR rep.

There technically is no difference

Sick days are saved for bona fide sicknesses. You can be reprimanded or fired for faking sickness.

Some companies give “personal days” which can be used for either sickness or vacation. This is fine, if you aren’t planning a vacation with all of your time, then get sick.