Have you ever gotten out of bed in the morning, and like me, have your husband or one of your kids say, "What happened to you there?" Pointing to a very obivious bruise. I spoke to my Dr. a couple of times re this, as sometimes I've actually just had what seemed to be spontaneous bruising-no bumps, or lumps! He told me that it can happen especially in the lower legs, ankles and feet areas due to blood pooling from crossed legs, so to watch that and try not to do that anymore. Upon further research, I've found that there are other reasons for this as well, and wanted to share this with you...Hugs, Teri 
"Certain dietary supplements such as fish oil, ginkgo, ginger and garlic also may increase your bruising risk, since these supplements have a blood-thinning effect. Make sure your doctor is aware of any supplements you're taking — especially if you're taking them along with a blood-thinning drug. Your doctor may recommend avoiding certain over-the-counter medications or supplements."
http://www.mayoclinic.com/invoke.cfm?id=HQ00355