What could cause a surge of hotness and shakes with feeling a bit dizzy and slow to talk, like someone's just injected you with pure caffeine, sugar?

Many things. could cause such spells, most common would be LOW blood sugar. Keep a careful diary of when they occur, what you are doing, when you had last eaten or drunk anything, and get an appointment to be seen soon if this is happening often. Obviously avoid caffeine, sugar, and try to eat frequent small meals that are high in protein and low in carbohydrates. Good luck!