Is it possible?

if you have natural wavy hair and then you had it straighten and then you want it to be wavy again? I tried it before but the salon told me that I STILL cannot do because she told me it would be bad for my hair. so when could I? I really regret having...

my hair straighten and I want my wavy hair back

if she only straightened it with a straightener then yes, you can get it back and no, its not bad for your hair
just have a shower and your hair should go back to being naturally wavy
if it doesnt try platting your wet hair then taking it out after a few hours (or leave it like that overnight) to get waves

If it was just a blow-out or she used a straightener, then a shower will get your hair back to normal.

If it was a permanent procedure, then it will only last a couple of months.

These things are obviously /not/ for life.

@pinkdottedbow, yeah you're right it was a permanent procedure and I didn't know that it was just for a couple of months I think I'll just wait for my hair to go back to normal. thanks to both of you : )