Does anyone have any tips for getting a short napper to sleep longer? My 4 month old ds always wakes after about 40 mins. I'm told that's when babies come out of a deep sleep. However, he needs a couple of hours at lunchtime and wakes up crying with tiredness but wont go back down. I try shush-patting, feeding, nappy change, anything, but he just screams. Any suggestions would be appreciated!