Hang it upside down to drain some more?

The standard recommendation is to only use a soft damp cloth and/or brush. The reason to avoid soaking is creating rust on the inside when, not if, it leaks in. Never heard of one instance deadening a head before.

I'd say there is 1) still some water in the head, or 2) you are imagining there is. Exposure to water isn't going to effect carbon fiber and titanium.

Simply use a damp towel to clean!
Swimming in water is no good!

Hope you can remedy the issue.

Cheers,
Dr. K

Im no expert, but golf clubs are made of hard materials such as ATI 425 aerospace titanium. I think if you got some water in there it would be a long while before there was any corrosion or rust. Its not made of paper so i don think the face is going to feel any softer or dead. Like I said I'm no expert so maybe someone more qualified could comment but I believe its probably all physiological for you at this point.

You quoted "slipped into sink when cleaning" but didn't clarify. If YOU slipped into the sink, you might have water in your ears and that will make it sound dead.