We have two cats - both elderly, both in good health. One of them (and I'm 90% certain which one) has recently started weeing and pooing around the house: for a couple of nights we would wake up with him having weed and pooed on the bathmat in the bathroom. We started lifting this off the floor at night, so he pooed on the floor anyway. We then closed the bathroom door while we were out, but came back to find he had weed on our bed instead. 
I think he is playing up because he is unsettled: we have been away on holiday (they stayed at home with someone coming in to feed them and clean up), and have had visitors. But this didn't start immediately after we were back, so it may be unrelated. We haven't changed anything else at all - litter tray in the same place, same litter, same tray, same food, same bowls...
What can we do to encourage him back to using the litter tray? We will be closing all the bedroom and bathroom doors until we are certain he is sorted, but that's preventative rather than curing the problem.
Any advice gratefully received!