For a long time, Thomas knew only darkness. The break in the void of his thoughts was just a hairline crack—only wide enough to let him know about the void itself. Somewhere on the edge of it all, he knew that he was supposed to be asleep, kept alive only so they could inspect his brain. Take it apart, probably slice by slice.
So he wasn't dead yet.
At some point as he floated in this confusing mass of blackness, he heard a voice. Calling his name.
After hearing Thomas several times, he finally decided to go after it, find it. He made himself move toward the voice.
Toward his name.