Shaking cat.

My cat, Misty will be 14 in Aug. The only problems she’s had until recently have been some ‘extra’ scratching (allergies?), also numerous sneezing at beginning of spring & fall, & when I got her at 7-8 wks. old she had a cold that was treated. Several yrs. ago, I’d noticed when she was ‘positioned’ for the #2 in the litter box, numerous times nothing would be there so I’d started her on higher fiber (dry) cat food.
My question mainly has to do with my cat’s shaking / trembling.
Abt. 1 ½ yrs. ago, I’d started seeing her head shaking every now & then; I continued to mention this to the vet & she would either say “I don’t know”, shrug her shoulders, or just ‘avoid’ the question.
Misty was diagnosed 2/19/13 as being diabetic; had noticed her drinking, peeing A LOT, was never overweight – (most she weighed was last fall was 8.2 lbs). She had also not been playing, seemed sluggish. I asked this same vet if this is why she’d been shaking/trembling and she ‘suddenly’ said “yes”. (I found her ‘sudden’ answer suspicious).
I was also told by this vet/her staff to give Misty some Karo.
(After trying both Lantus and also a diabetic – prescript. diab. cat food & neither seemed to work very well – she had diarrhea & would then throw up while on diab. food, the same vet said “I just don’t know what to do” – so I changed vets.)
I’ve been taking Misty to another vet; her put her back on the Lantus at only ½ unit to start, once/day & she’s now up to 1 unit in a.m., ½ in p.m. & showed me how to test her at home to check her Glucose level.
I found out that Misty’s shaking doesn’t seem to be from her Gluc. level. She’s continuing to shake/tremor – more often, and many times you can tell it is her whole body. She will still walk around, a little, or turn over on her side, and you can definitely see that all her legs are also shaking. These times can last 10-15 sec. to 15-20 minutes.
Many times, I’ve just happened to have tested her Gluc. & it was anywhere from 200-High.
I have also asked her newer vet a couple times about the shaking and again, am not getting an answer as to what it could be – I’m thinking something neurological, but it seems like vets don’t want to answer it.
Misty did have an ultrasound on 5/17 and there was a cyst on her pancreas; she’s scheduled for another partial US on 6/17.
She is back on regular dry cat food & also canned food, but still has some diarrhea/looser stools w/blood/mucus in it – was diagnosed as colitis
Her wt. is now down to 5.15. (She’s also on Mirtazipine to ‘boost’ her appetite). She seems to want to play at times, but really hasn’t since a short while before being diagnosed w/diabetes. Am not sure if it’s because she’s ‘trembling’ so much & more often, or her gluc. level.still not always being stable. Her trembling used to be just every once in a great while. Now it’s a pretty regular thing – a day or 2 may go by when you don’t see her ‘shaking’, but you can easily spot it (3-4 x’s/day) on a pretty regular basis – at times from a 10-12 ft distance.
I realize you can’t give any definite answer, but re: her shaking so often,are there things I need to be watching for or ask the vet to do? Thank you. (sorry this was so long)

Yeah, Misty really has been going through a lot. Had actually wondered about seizures myself because I've had them for decades although don't anymore. Yet you mostly see grand mal seiz. described in seizures for cats.
Your reply was truly appreciated & helpful Thank you so much!