free-floating anxiety = anxiety unrelated to specific circumstances
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He is full of adrenaline, his nerves are shot, and his mind is cluttered up with free-floating anxiety-floating around on an ocean of generalized terror.†
(source)
Neal Stephenson, Snow Crash, 1992
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Fear of such judgment may be feeding the free-floating anxiety that we have found, which manifests itself in adamant doctrines of correctness and the firm conviction that "other people" are ruining the language.†
(source)
Robert MacNeil and William Crane, Do You Speak American?, 2005