It is really the only thing I ever select cosmic magic for.
I would pay 3 solid character points and way more mana (probably as much as eight) to gain this status effect.
It is certainly a lot more powerful and useful then gravity / flight and certainly deserves to be swapped with them.
I don't know if you have coded this to set the MP cost for each inverse spell seperately but you should certainly consider really REALLY jacking it up if you can.
I feel that mana cost is a much better way to balance this spell than duration because duration is somewhat easy to extend and very hard to balance (see: invisibility) whereas you will always need mana resources to stay alive and should be somewhat paranoid about burning through it. At least I am.
I know the way things stand now I always pump my mana into it when it expires for my longest and best playthrough attempts and my deaths can almost always be attributed to forgetting to maintain it. Now that's power.