Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine your husband and obtain a history, I can not tell you what the exact cause of his symptoms is. However I will try to provide you with some useful information.
Identifying the potential causes of your husband's symptoms of leg shaking is difficult without being able to view the shaking myself. Seziures are certainly one potential cause of leg shaking in general. Seizures are best diagnosed if the leg shaking is observed and fit with a seizure and/or if a brain wave study called an EEG is done during an actual episode of shaking. However, since the tremors only occur at night when he is lying down, seizures become less likely. Seizures are a potential diagnosis if the shaking is thought to be coming from the brain.
However, the spinal cord and even the peripheral nerves can be a cause of shaking as well, in which case this would not be called seizures. Other types of shaking occurring due to spinal cord or peripheral nerve problems include myoclonus and clonus. If your husband has disc disease of his spinal column which affects the spinal cord or nerves as they exit the spine, then this would potentially explain the tremors. Other points of historical important would include whether or not he has weakness or sensory loss in his leg.
I recommend that you follow-up soon with your neurologist, particularly if your husband is having weakness and/or numbness in his leg which would signify potential spinal cord or nerve involvement from his disc. If the episodes of shaking are consistent but would not be reproducible in your neurologist's clinic, it might be a good idea to video tape them so your neurologist knows what they appear like. Follow-up with your husband's surgeon is also important. Depending on the neurologist's and/or surgeon's findings on physical examination, additional testing including MRI of the brain or spine (Depending on what whether or not it is thought your husband's symptoms are seizures or from the spine) and/or a study of the nerves called an EMG/NCS may be ordered.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
I forgot! My husband also had am MRA which is like an MRI of the brain (4 years ago) and ruled out MS. He does not have MS, MD, or Parkinsons.