dangerous wiper problem!!!!!

hi all

got a problem with the wipers slowing down then stopping completely in heavy rain,i say this is dangerous because it happened yesterday on the motorway in a torrential downpour.after pulling over and waiting for a while they started again.could this be a water drainage problem ???? ie motor getting flooded????. I have just spent 15 mins on the drive with wipers on full speed and no problem at all ?????

any suggestions please