16 month old waking in the middle of the night

Our daughter started falling asleep on her own at 4 months and has been sleeping through the night since 8 months. She has always been a GREAT sleeper. But the past 2 weeks she has been waking up crying between 1-3 AM, and won't go back to sleep unless my husband or I lays down beside her crib. Once we do that, she settles right down and goes back to sleep. We don't mind doing it if it's just a phase and she needs a little extra comfort, but we also don't want to start any negative sleep habits.

Anyone else gone through this? How long did it last and how did you get through it?

Also, she doesn't do it every single night. About 25% of the time she will still sleep through the night, but most nights she wakes up.