Why does my rabbit shake?

Question
Her name is "cuddles". She is adorable...(what rabbit isn't)     I have her from 2005. She was abandoned and we took her in. We went thru a few scary times. We dealt with hairballs a few times and had to get her spayed, which was a good thing because afterwards we found out there was cancer within the uterus but it did not spread.
Her diet is very simple. Unlimited Timothy Hay and no more then 1/2 cup of pellets. A few treats now and then also.
Her poops and pees are normal. She drinks water normal.
That's a brief history of her. Here's where I'm puzzled...
At times she'll hide in the corner of her pen and start to shake.
It's not from running or binking. It's always at night time or early morning. She'll shake anywhere from 1/2 hour to 4 hours and then she stops like nothing ever happen. She'll start to groom herself and hop around and even eat afterwards. She'll go 6 - 7 days without any shaking and then it will happen again.
This been going on for a few months. Could it be something to do with her shedding?
Any thoughts?
Thanks for your time.....

Answer
Hi There

Usually I have heard of rabbits shaking from fear, being cold or pain. Have you checked her over head to toe to ensure she isn't uncomfortable in anyway? Look in her mouth, massage her ears, especially close to her head. Rabbits are prone to problems in their teeth and ears. Look at his belly and pet him with gentle pressure. Does his abdomen seem distended, or does he suddenly pull away anywhere when you are touching her.

Is she eating and eliminating as usual, without any diarrhea. does she have any sticky fur that has urine or feces stuck to it when you look at her genitals?

What are you feeding?

Do you have air conditioning still? Are any windows open or have you recently vacuumed when this happens. Anything else that might be perceived as frightful to bunny?

I don't think it has to do with shedding. Let me know your answers and it may narrow this down.

Alice