It is a Growth Spurt!

There are probably a lot of things your mom told you about babies that turned out to be old wifes' tales. Here's one that's true! When your baby sleeps a lot more than usual, it really is a growth spurt! I remember the days when I would all of the sudden get four to five hours of sleep at night and a three hour nap during the day! It was amazing! I LOVE growth spurts!
FROM NBC: Moms have said it for years... now science confirms that when babies sleep a lot for a few days.. they're going through a growth spurt! Emory University researchers had 23 parents keep daily sleep records for their babies -- from the newborn phase throughout the first year. They found measurable growth spurts right after intermittent periods when babies took more naps and slept longer. This may be reassuring to parents -- who can become frustrated by the unpredictability of infants' sleep schedules. Researchers say hormones released during sleep might account for the growing phases.