4 mo old waking up crying?

Samantha • Leila Jade's mommy 👶🏼💘
My 4 month old woke up from her nap randomly crying really hard like she was hurt or scared and I know she wasn't hurt bc I was watching her the whole time ... now I'm rocking her to sleep and she just randomly started the loud very sad cry again:( I feel so bad I have no idea what's wrong? Teething pain? Bad dreams? Any ideas ladies ?