How bad are cysts???

Hey I know this is a dumb question to ask. I was at my ob about 2 weeks ago cause of abnormal periods and because of major cramping. My ob ordered a sonogram and wanted to see if everything was ok. When i was 9 months old I had a hernia operation on both my ovaries and she wanted to double check and make sure that i didn't have one of those again. Well I went back there and that's when i found out that i have a cyst on my right ovary that's 2 cm in diameter. My ob told me not to get worried till its 4 or 5 cm in diameter. My question is will it go away or will it get worse?? I'm sitting here stressing and not sure what it is or anything like that. She told me not to stress out about it but, i can't help it. I take everything for granted and don't take things lightly when i find out something like this is going to happen. I'm only 28 yrs old and really don't want a hysterectomy yet!! Please help me calm down and not stress out so much!!