copied and pasted from babycentre:
Sleepy baby
Babies come in all shapes and sizes, and they have very different feeding patterns. Some are frequent feeders, some have large gaps between feeds, and of course there are many variations in between.
Most babies tend to sleep a lot in the first 24 hours after delivery. They are often very alert and ready for a feed immediately after the birth, but then take a long rest. If you were given pethidine or other drugs during your delivery, they may have passed through to the placenta and your baby may be sleepy until the effects of the drugs wear off.
However, some babies continue to sleep a lot in the early days, which means they don?t feed often enough and so don?t get the milk they need to thrive. Too many long sleeps can result in a vicious circle developing, where the baby doesn?t get enough milk to give him the energy to wake up at the right time for the next feed.
Your baby needs to get plenty of fluids to gain weight and he also needs to feed regularly for you to establish breastfeeding, so it?s best not to let him sleep through too many meals. Ask your midwife or GP to check his progress.
Remedies
If your baby is sleepy, try the following to stir him:
Change his nappy
Wipe his face with a cool face cloth
Remove his clothing down to his vest
Look for signs that he is stirring or in a light sleep and wake him, then
Squeeze breast milk into his mouth to get him interested