I have put unexplained in inverted commas because I am quite clumsy and often cannot remember when I knocked into something.
However I have a huge bruise on my arm which is quite sore-I would have thought that I would remember that-and I have a bruise on top of my hand-again I have no recollection and that is quite a difficult area to bruise so I would expect to remember.
Google suggests it can be an effect of ageing - I turned 50 this year 
So I suspect it is not that
I have lost a significant amount of weight, but quite slowly -nothing dramatic and within healthy BMI, so not excessive.
Any one else experienced this?