Chin collapsing and convulsing - HELP!

I've just joined the forum as I really need some advice!
Our girl Flo (c.4 year old standard grey) has been collapsing/seizing regularly during play time in the last 2 weeks.
I took her to the vet on Monday and they diagnosed a heart murmur, and said she needs to lose a bit of weight (she was 770g). Advice was to avoid long periods of exercise and increase hay consumption by reducing pellet feed.
Now, I might be wrong but I'm just not convinced that the heart murmur is the culprit here.
The episodes happen pretty quickly after she gets out to exercise (before she's really exerted herself).
She will suddenly start to move differently to normal (lower to the ground, almost like a soldier's crawl?!) and then just flop on her front. She goes limp and doesn't object at all when I pick her up (normally she would complain and wriggle!). During the episode she will shuffle about the room a bit but is clearly disorientated and uncoordinated (like she's drunk). Her eyes mostly look normal, maybe a bit dozy. But she is not totally unconscious and does react (mutedly) to noises, etc.
Last night was the worst though - after she flopped I laid her in my lap and then she started convulsing (her head would visibly pull upwards and back in a spasm) and she made what I call her 'squeaky toy' noise (warning call). She did this about 3 times and then just sat around looking dazed.
During previous episodes she has trembled a bit and occasionally juddered (like she had hiccups?!) but never a properly jerky movement like this, and never any vocalising!
The episodes generally last a couple of minutes at a time but they seem to be getting longer (last night she was out of it for at least 5 minutes). However, it does pass and then she seems totally fine - alert, bright eyed, eating and pooping normally.
Does this sound like it could be a heart murmur? I'm wondering if it could be hypoglycemia (although would it be weird to happen so quickly after I let her out, and stop without any sugary treat?). Or possibly a thiamine deficiency? Pretty sure its not calcium as her teeth are a healthy dark orange color. No big changes to her feeding patterns or routine recently so I don't think its environmental.
I'm wondering if I should stop letting her out of her cage for a week or two as it doesn't seem to happen until she's out and about!
I plan to take her back to the vet unless things improve but I don't really think any of the ones near me are super-experienced with chins, so if I can go armed with suggestions I'd be happier.
All thoughts gratefully received!
Thanks,
Jenny

I would either stop offering playtime or give her a raisin or goji berry just before playtime to see if that makes any difference.

770g doesn't sound very overweight to me, but I have no experience with heart murmors, so I'm not sure what ideal weight for a chinchilla with a heart murmor is.

There is no "ideal" weight for a chin, other than if they are obviously underweight and needing to put weight on. I have chins that are normal at 600 and others that are normal at 1100. It depends on genetics, they are not one size fits all.

My first chin had both seizures and a heart murmur. And it sounds fairly similar to what you described. If it keeps happening when hes out then stop letting him out.

Something might be 'triggering' these reactions in him. Certain things might set it off. For my chin, it was seeing his girl (in a diff cage or out for play time) and not being able to get to her. It got him so worked up that it would start seizing. So think about each time its happen and try to find commonalities and eliminate them.

It does sound like a low blood sugar seizure, the mild shakes and collapse, the disorientation and drunk crawl. The murmur would IMO produce the same symptoms except the shakes-that and it would have to be a class 4 or higher to produce symptoms. As a side note, do you know the class? I have seen chins get themselves worked up in a short time and seize with no real exercise. Have you tried to get her out of the seizure with something like karo syrup or honey? Apply some to the front of her incisors or inside her lips when she is seizing or if you are not comfortable with that give her a bit of something to eat before she plays, a bit of something sweet-I used to use baby food on a shredded wheat, and see if that helps. If not it could be the seizure is produced from a unknown nature-it can be treated on a seizure by seizure basis with valium or Diaulatin daily if they are too frequent.

Thank you all for your thoughts.

I tried letting Flo out this evening about 5 minutes after giving her a raisin but unfortunately she had another collapse after just a few mins of hopping about, so maybe it's the heart murmur after all as the sugar hit doesn't seem to have made a difference. I tried to rub some honey on her gums when she was collapsed - it had no effect but I think I maybe got more on her fur than in her mouth so it's hard to say!

She is hopping about her cage normally again now but she does seem to be very tired for this time of the evening so the seizures must be taking it out of her, poor thing!

I am beginning to think you're right about not offering play time - whenever she is in the cage and hasn't been let out she always seems fine. I'm wondering now if she just gets really excited about being able to run free around the room and that's what brings on the attacks. But I feel so mean not letting her play out and I know that a lack of exercise can cause other problems with weight and digestion, so it's a bit of a catch 22! She's never used a wheel (I got her a flying saucer one but she never seemed interested), so any advice for how I can exercise her while limiting play time?

I have racked my brains about environmental stimuli but I can't think of anything that has changed in recent weeks to bring on the behaviour. Flo never got on with other chins so she has always been on her own (with lots of human attention!) so it's definitely nothing to do with that. But maybe as I said above it's just the excitement of being out of the cage that's doing it.

In terms of her weight, it's reassuring that she might not be as overweight as the vet suggested. She's always been well exercised and given plenty of hay along with her pellets and limited treats so I was a bit confused about how that could have happened!

The vet said he wanted to X-ray her to see the heart murmur - I am reluctant though as I don't think being sedated/anaesthetised will be good for her heart! Also he said they can't give any medication for heart murmur so I don't really see the point in putting her through the stress? I don't know the class of murmur but I know both the emergency and exotics vets confirmed it very quickly when they listened to her heart.

Who knows!!

Thanks all. Tried letting her out last night after feeding a raisin but the same thing happened, so I am thinking it probably is the murmur that's doing it. I think I am going to have to severely limit her play time as she always seems totally fine until she comes out! Maybe she just gets really excited and that is the trigger. I feel so mean keeping her cooped up though - she loves being out so much! Also I am a bit concerned that reducing play time will lead to other issues (e.g. Digestion problems)?!