eerie book ending

I'm still creeped out by this, from James Rollins' Ice Hunt:

6:55 A.M.
UNDER THE ICE...

The tank rested on the ocean floor, full of water, crushed and cracked. The lone occupant was a frozen lump of bone and hardened tissue. There was no light. No sound.

None could hear the screaming inside the man's head.

The cryoprotectant had worked, preserving and protecting him. But there was a side effect he had not anticipated. A horrible, monstrous side effect. The figure now understood the years the Russian scientists had spent researching sedatives and soporifics. Sleep drugs. The research was not ancillary, but critical to the suspended animation.

For the state created by the elixir was not sleep.

Consciousness remained--frozen, too, but intact.

Sleep was denied him.

He screamed and screamed, but even he heard nothing.

Deaf, dumb, blind.

Yet his body remained, preserved for all time. Deep in the black depths of the Arctic Ocean, one thought persisted as madness ate at what was left of him.

How long? How long is eternity?