Let baby sleep

Dr said not to wake up baby at night n let him sleep until he wakes up. Trouble is, now after being on a 1.5 hr sleep schedule for 1 month, and tonight after having slept 3-4 hours straight, I'm wide awake. I'm grateful that he's able to go this long without a feed, bc if (touch wood) every night is like this, my life will be 'normal' again. I just have to get used to not being sleep deprived!