The Vortigaunts call it "the interval of darkness." At least they do in English; "darkness" isn't quite the right word for it. A soul detached from a physical body has no eyes with which to perceive light or the lack thereof. Without ears there is neither noise nor silence. Without a nose or mouth, taste and smell are impossible. Without a nervous system, there can be no feeling or even a sense of a body.
'No senses' is not the same as 'no perceptions,' though. Not by a long shot.
And she perceives... everything. The whole of Creation is laid out before her. And behind her, and around her, and through her. An infinitely complex tapestry of worlds and thoughts and energies, ever moving, ever changing, but always connected, spun out in every direction across the neverending space that is not space, the time that is not time.
One lone human being could never hope to comprehend it all. But it would be so easy to let go of being one lone human being, to disengage the patterns of her own substance and flow back into the tapestry...
Don't go.
It's not speech; speech implies a voice, and a voice implies sound, and sound implies the ability to hear. But there is a presence that's trying to communicate. Please, it tells her, voicelessly, wordlessly. Please don't go. I need you, Alyx.
Being called by her name brings her back into herself, if only for a moment. She remembers. Remembers a clearing in the forest, with trains and tall buildings. Remembers a creature, alien and predatory, leaping down on her from above. Remembers a piercing pain in her chest and back. Remembers his look of horror as he tried to reach out for her, just before everything faded away.
Am I dead?
No. There's urgency in the not!voice. Just hold on. Please.
Hold on? To what?? There's nothing solid, nothing stable, nothing even recognizable. How long can she hold herself together in the face of this?
Desperately, she casts out for anything familiar, anything to which she might anchor herself. For a moment/hour/year/eon (time is meaningless here) she finds nothing.
But... wait. That feels familiar. A pocket of time outside of time, space outside of space, connected to all but sheltered from the infinite that threatens to overwhelm her.
How she moves, she couldn't say, but move she does, sliding between the threads of the tapestry to reach her
safe haven.