Baby falls asleep mid cry?

Agnes
My little girl is almost 5 months old. The last few days, she's started to get fussier when I put her down for a nap or for the night. One time, I was really frustrated so I decided to just walk away for a few minutes, and I heard her literally fall asleep mid-cry - she was crying, and then it was cut off and silence. I checked on her and she was fast asleep, and slept her usual length nap. I've now had her do this several times, usually after only a few minutes (less than 5) of crying. 
Is this bad? She seems fine when she wakes up and is her usual happy, smiley self. I've read that cry it out shouldn't be tried before 6 months, and that wasn't my intention but it seems I've inadvertently used that method on her too early.