It does sound like SM related problems, get to a neurologist and get an MRI done, at least that way you will know whats gong on.
The only problem though with a mini scan is the area being covered is only the head and top neck.
Although unusual 1 Cavalier has gone through an MRI scan in Swindon (on M4 junction 15, at the Great Western Referrals, the scanner calls in evey Monday, neurologist on site but scans can also be sent to Geoff or Clare for written report, although one given with results) with a very low syrinx only. This would have been missed with a mini scan.
The dog went for a disc problem and SM was picked up then.
Although uncommon, it's worth noting. If you can get a full scan then it's preferable.