Help!? my Platy fish wont stop spinning?

[Platy_Lover]

Hi. I have a 50 liter tank which currently houses ten fish. It is not overcrowded as i have checked with the lfs. I have a Female Parrot Platy who has started to spin almost as though it is uncontrollable and when she does stop, she lays on her side on the gravel. None of the other fish are doing this and show no signs of any illness. I don't overfeed and i do regular water changes (1 a week) of about 10-25%. I check the water is the right temperature and that i have added water conditioner. I don't know what this could be, please, if you have any ideas let me know

Thanks,

Platy_Lover