That's why I think this is more likely to be pain/neurology related. This kind of randomness is typical of CM/SM pain. A lot of CMSM dogs show more difficulty at night -- scratch more, have pain episodes then. The drooling is I think what I would find alarming -- he must really work himself into quite a state. Drooling at that severity would generally be from anxiety, pain or medical-issues. Or a mix?
but why only at night, and why only a couple of times, with a 6-8 week gap in between them? He's now had 3 episodes while I've been sitting during the day, and 11 after being put to bed.