My cat does this sometimes (about 3 times in the 6 months we have had him), it is quite normal, especially around this time of year, as even indoor cats start to develop their winter coat about now, so much more fur for them to swallow when cleaning themselves, thats all it is, furballs.
He did it once straight after eating his food, (we feed him a very small amount of meat and the rest of the food is crunchy biscuits) but as already mentioned it was totally undigested, so i guess he rushed his food that day and that was why, plus he hasn't done it since.
He is good though, as although he didnt quite make it the first time it happened, he does get up and move from the carpet in the opposite corner of the lounge by the radiator where he sleeps all the way through the room and into the kitchen where its all lino.
Now, if only we could stop him doing a wee on any soft furnishings in the flat at night or when we are out then i would be very happy, sofas, cushions, our bed, my jacket that he clawed off the back of the chair onto the floor one night, a black bag with clothes ready for washing, towels in the bathroom, etc... anywhere soft.
Everyone i have spoke to says we should get him neutered, but he cant be neutered, as he has a heart murmor, and according to the vets, the risk of putting him under to do the procedure and him not waking up again due to his heart is too great.