My old cat was jerking, seems fine now?

i have a 15 yr. old manx &  tonight after she ate she came into the L room and i happened to look over at her and she was jerking, her whole body was jerking and kind of coughing? lasted maybe 10 or 15 seconds. never saw that before... she is on sci diet (KD for low protein) and there are no toxins in my house.
she was upright and at first i thought she was gonna hack up a hairball! but that was not it.
i went over and checked her, there were no other symptoms, and now she seems fine. i don't think i can take losing another friend right now- and specially her, she is really the sweetest thing in my life. i am freaking out. she just had a physical and checked out fine, but he did say he heard a very slight heart murmur.
any suggestions? ideas? i just lost so many of my pets- i am trying to keep her well as long as possible.
thanks all y'all!

[opus88]

first of all I am soooo pleased that Bali got a clean bill of health from the Vet...

I don't know what this new development could be other than a seizure or an asthma attack or simply trying to dislodge a hairball? I am sending a site on asthma, scroll down and click on the WMV video, the first one...it shows a kitty having an attack watch this and see if this looks similar. if not than I think it was possibly a seizure...perhaps brought on by the truama of going to the Vets and all the handling?

I sure hope its not going to be anything so serious, I know you've been through an awful lot lately...sending some ((hugs))