Why Was Master Yoda So Knackered In This? Stroke? Plot Hole?

It doesn't really make much sense that Yoda was so completely knackered in this.

We see him in Revenge Of The Sith bouncing off walls, tossing about senate seating booths like they were nothing, etc yet here he is like a senile old man and then he just carks it...

Yet he's been training Jedi for over eight hundred years, so the twenty years or so between ROTS and ROTJ should really be almost nothing in terms of Yoda's lifespan.

So what gives? How come he was so knackered? Did he have a major stroke at some point not long after landing in Degobah or do we have to accept the possibility that we may be looking at a major plot hole here?