If its only during the night, I doubt it has to do anything with physiological pain. Or it has to do with mechanical difference like laying down for a long time that her stomach acid boils up or so.
So assuming its not physiological, I would like to share the following with you.
If you don't do so already, this might help, it certainly won't hurt:
The moment it happens is crucial to note your own feelings, especially when you enter the room. Children haven't a well established sense of language yet and so they are more sensitive to emotion than to what you say. For example. If you would say "calm my dear, its all right." but you are feeling stresses/agitated, or whatever emotion that is not radiating comfort, you might not be of any help or even make it worse. So besides telling her its all right, let her feel its all right as well. Make her feel its all right whats she is going through by giving her the feeling that you do understand, but give her the feeling that its not something she should feel stressed about. The latter should make her feel she can trust you on this one, so she can try to let it go, as you are there when 'things go wrong'. When you show you understand she can't feel 'bad' about herself. Negative self-reflection like feelings of 'i'm silly' or 'it's not good what I am doing' or 'parents do not like me when I do this' should be avoided by showing that you understand.
She is a individual, developing her self, and it's her responsibility to overcome this. It's a matter of INTERNAL change. Therefore, I would not recommend you visit a 'professional' so soon. As this might give here the feeling that something is wrong with her, that needs to be fixed (externally). If that idea penetrates her mind, then she has just build a mental blockage, and likely isn't able to solve the problem herself anymore. In fact there isn't anything wrong at all (probably). It most likely is just a matter of growing up and her perspective needs to be adjusted to the new things she is capable of (viewing the world, seeing certain patterns, feeling certain emotions and what not).
Have faith and confidence that she is more than capable of resolving this issue by herself. Give her at least the change to do so by being supportive.