The formation of this cyst is not a very serious health problem. A Baker's cyst in most people goes away on its own. However, if the cyst stays for long, it can cause considerable discomfort to a person. This cyst can also create problems, if it gets ruptured. A ruptured cyst will cause pain, swelling, and bruising in the affected part. If you have a lump behind your knee region, it is most probably a Baker's cyst which needs to be checked by a medical practitioner.