joints after mini layoff

hi all

just a silly curiousity question.  i've been exercising regularly and pretty strenuously for a while now.  i just was away for the last three days and really didnt do anything aerobic wise.  today, i feel it in my joints - not sore or hurting - they feel kind of funny and lazy - not sure how else to describe it.  was just curious if theres some scientific or chemical reason for this - any one have a clue what im talking about?