His muscles were atrophied: even were all his injuries healed in an instant (and though it was possible, he would never let it be so) he would need a century of physiotherapy to be back to a modicum of the old strength. He knew this.
He knew all. He knew he was damaged, that his Empire was damaged, that he was doomed - that his throne was slowly failing. He knew the names of every Chapter of Space Marines. He knew every secret of the Blood Ravens, every thought of Marneus Calgar on Macragge, he knew what Cypher sought and that he was probably going to get it (indeed, some small part of his consciousness had been storing the energy to stop time for the admittance of the fallen angel into the inner sanctum for some time). He even knew the mind of Alpharius, the thoughts of Abaddon, the plots of Ahriman and Bile.
When one can do nothing but stretch ones mind across a cosmos (and indeed when that very stretching is keeping your species alive), one learns to eavesdrop on what one would want to know. However, he did try and leave some mysteries. He didn't know, for example, just what was healing Roboute Guilliman (he hazarded a guess at a flaw in the stasis chamber that was letting the Primarch's enhanced systems have a fighting chance) but it certainly wasn't him, though a lot of people thought it was. Nor did he know who all te Legion Of The Damned were (some of them were Fire Hawks but not all). Nor did he know where exactly Jaghatai Khan, Vulkan or Corax had buggered off to (first thing I'm going to do when they fix my vocal cords - if they ever get round to fixing my vocal cords - is swear like a trooper) nor did he want to. Corax had felt guilty and had needed to work off some steam, and was probably dead. Vulkan's absence was totally random and inexplicable, just as the Emperor preferred it (he really didn't want to know everything).
There wasn't much an Emperor could do when he was stuck on a throne. He could of course complain to the Custodes once in a while, or he used to before the ones he complained to started committing suicide. He could cause the odd vision, influence the odd Emperor's Tarot (though he kept to the tarot's that were important, like the remains of the Fire Hawks and the Grey Knights) and keep people from dying occasionally (again, the Fire Hawks, who would have died before they figured out how to be useful otherwise). He could observe, cause Warp Storms (like the one he cause when Vandire was in charge, bloated opportunistic bastard that he was), occasionally create the odd miracle.
He was bored out of his mind most of the time though (and considering his mind was currently the size of a galaxy, that was difficult). After all, once upon a time he had the ability to walk, kill with a sword (and not just his mind), guide his Imperium in person instead of gritting his teeth at the many fuckups they all made in his name, and most importantly, have a beer once in a while (he might not have had Leman Russ's appetite for alcohol, but that didn't mean he didn't like it).
Now he could occasionally stop time, shit (metaphorically) psycannon ammo, create the Astronomican and - well, that was it. There was nothing more to life.
If this was life and not just a lingering death.
He sighed mentally as another day (or week, or month, or whatever it was) wore on. Finally, he snapped and started thinking something random.
"Ninety nine bottles of Recaf on the wall, ninety nine bottles of Recaf..."
Well he had to pass time somehow.