There is a on-screen (and relatively easy to accidentally click) short cut to Free Look condition, which is what you are describing. You should be able to undo it by sitting or by using the shortcut key for putting the camera back on follow (I think it's keypad7). I use mouse for movement and can get out of this condition by holding down the L and R buttons at the same time.
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Remembering Tyneetryk
Phaedreas Tears - 15 years old and first(*) of true neutral guilds in Atys.
(*) This statement is contested, but we are certainly the longest lasting.
<clowns | me & you | jokers>