Anxious at night time.

Okay, So this is a slightly weird question but it is one that is extremely pressing
We have 2 Shih Tzu's, Molly & Max, That we have had basically no issues with, until a few months ago, When out the blue, Molly changed totally, Not in the day time, in the day she is totally normal, absolutely fine, responds to call well (always has) However at around 2am, every night, she suddenly becomes this different dog, it is seriously becoming an issue, it is 6am in the morning and I am writing this message because I'm unable to sleep (Due to the noise), Okay, so to explain, well, basically she scratches at the back door to go out, however where it gets so cold we can't let her out (The times when she gets out, she sits, for hours, shivering from the cold not moving). She begins to pant as well, as soon as it gets late, and the worst thing is, she suddenly stops acknowledging you, like totally, you can yell, offer treats , and you get absolutely no response, when in the day, she is pretty obedient, She also tries to lock her self in the utility room by wedging the door shut, and then scratches on the door, the only thing is, once you come down stairs (We've tried ignoring for days with no luck) she continues to pants and stratch, and spends her time scratching at the front and back doors, We've been extremely patient with it and have tried both positive and negative reinforcement, we've tried taking her on walks before bed, we've tried everything, but it is absolutely beyond our capacity to deal with anymore, She also tries to pull down the baby gate we have at the bottom of the stairs and cries at it, Our other shih tzu, Max, is totally fine, She has never had any anxiety before, and it doesn't appear to be the case now, we've even tried to offer her her favourite treats to see how unresponsive she becomes, and she doesn't even sniff it, Literally no response,

A friend of ours suggested a parasite of some kind

please help!