My 4-mo-old LO has had a really tough time sleeping overnight generally. This week, though, it's been really bad. I thought it was a reaction to his shots last week. He started daycare last week and sleeps really well there, so I asked them what their secret is. Apparently they think he's cold, so they double swaddle.
So I attempted the same set-up at home, and he slept great! Finally.
I told other moms in my playgroup about this, and more than one said that their child was also having trouble sleeping. They also remembered that they hadn't opened up the heat vents yet in their LO's rooms. My friend tried the same double swaddle, and her son also slept great finally.
So, heads up. Now that it's colder in many places, make sure your LO is warm enough, and you may benefit from more sleep!