No worse than normal, at least for me. I found the experience dull. Always having some internal auditory stimulation may have been part of the cause of that.
Also, I meditate very easily and prefer a whitenoise environment for meditation. And I'm very happy in my own head and used to being alone. So the whole thing was not much a novelty in any respect, and the lack of whitenoise made it suboptimal for meditation.
I wonder how people's response to these things varies as they move along the extroverion-introversion scale. It seems plausible that extroverts would find them a much more novel and disturbing experience than introverts.
The fact that a float tank would never be true sensory deprivation makes me sad.
Having tinnitus drives me crazy. Not in literal sense, it's not like I focus on it all the time. But at night when I hear the crickets and other nightlife, I mourn the lack of silence in my head.