He experienced no physical change, but for a half a second, Lex blacked out. His mind shut down from the sheer extent of the despair he was forced to experience as a self defense mechanism. It worked, and he was saved. But the problem was that he was in the middle of a storm, and so the moment he woke up from his blackout, he was hit by another wail, causing him to fall into another blackout.
Giselle noticed that something was wrong with Lex, and moved to surround him with a protective bubble. Yet before she could do anything, Lex woke up again, and immediately activated Mindmeld.
This was an ability he gained which allowed him to turn into thought itself. Or another way of putting it was that he gave up his physical form to whatever extent he wanted and turned it into the same spiritual energy which made up this storm.
