Thank you for your query.
There could be various conditions you are describing.
Often, during the normal menstrual cycle, after ovulation, the remaining tissue is converted into a corpus luteum
Corpus luteal rupture is common.
Often haemorrhagic cysts occur in the ovary due to rupture of a big sized follicle.
Endometriotic cysts rarely rupture.
In order to tell you how dangerous it is, and what exactly is happening out there, you need to give specific clinical details and ultrasound