Hello Mairead, I'm Dr. Deb.
I recently came online and see that your question about Elsie hasn't been answered. I'm so sorry that you've had to wait for a response,but if you still need assistance, I'd like to help if I can.
1. My first thought after reading your description of her behavior was that Elsie may be having partial seizure or petit mal seizure episodes ...and I suppose this is still possible...but usually these episodes aren't painful. If her vocalization is reflective of confusion about what's going on with her body, then this might still be a possibility.
Unfortunately, such a problem is going to be very difficult to specifically diagnose and will be one of ruling out other issues first.
These kinds of seizures do not typically progress into grand mal seizures or epilepsy. They tend to remain as they initially present. They will continue for the life of the cat, in most cases.
I typically don't treat these cats with anti-seizure drugs unless the episodes occur more frequently than you describe.
As to the underlying cause, more often than not they are Idiopathic...meaning we can't find a reason for them. As a result, we are not able to prevent them.
2. The other possibility is that there is some issue with her spine such that there's compression of her spinal cord. Your description isn't entirely consistent with this problem, though, since the episodes typically last longer than just a few seconds.
X-rays might be suggestive although typically an MRI is needed to specifically diagnose such an issue.
I can understand why you might think a trapped nerve is the problem but, again, I would expect the episodes to last longer.
3. There are other diseases such as Toxoplasmosis or FIP which can cause neurologic issues but, again, they usually last much longer than just a few seconds.
4. An issue with her heart such that her circulation is affected is another consideration, especially since you indicate they primarily occur after play. A good physical exam might detect a heart murmur or an x-ray and/or echocardiogram may be suggested.
5. I've seen some cats with gastrointestinal pain assume a position similar to what you're seeing but I keep coming back to how long her episodes last....cats with abdominal pain are usually experiencing discomfort for longer periods of time.
If you have not already done so (and if it's possible), it might be helpful to tape or film the episode the next time it happens so that you can share this with your vet. If the episodes are increasing, then it might be prudent to have her seen.
I hope this helps; again, my apologies for the delayed reply. Deb