“Are ovarian cysts a serious condition?”

It depends. Factors one may consider include size, sonographic or other radiologic findings relating to the cyst. Also, biomarkers are available to triage the malignant or benign nature of the cyst. Notwithstanding, the majority of ovarian cysts are benign, but this must be thoroughly worked up.

Typically, the ultrasound is repeated after an appropriate interval usually 4-8 weeks. If cysts are related to a particular time in the menstrual cycle like after ovulation, then those typically resolve within 3 months and are not of concern. Other cysts depending on appearance may be left alone and observed. In others, additional testing such as lab work for tumor markers may be done. Depending on your age, appearance of cyst, whether or not menopause has occurred, family history, and symptoms is what determines whether a cyst is serious enough to have surgery.

The majority at your age are functional, i.e., benign. But some are tumors (mostly innocent) & some are endometriosis. You need to repeat the ultrasound after 3 month. If the cyst disappears, then it is functional.  

It depends on the morphology of the cyst. Most cysts are benign but the lifetime risk of developing ovarian cancer in the USA is around 1:70.