Can someone who has DID explain what the term "drifting" might mean?

The last couple of times I've spoken to my friend on the phone, he will begin talking very low, with long pauses in between talking. When I ask him if he is tired, he says no, but his body is "drifting." I've asked him what he means by this but he's never been able to explain it...esp since the times I've asked he is "drifting."

To me he sounds like he is falling asleep, but I wonder if he might be "drifting" into his alter.

I will ask him about it further when he is more lucid, but I was wondering in the meantime if anyone else knows what this means or can explain to me how it feels.