I'm bipolar, and use the cards as therapy myself. I haven't had a serious depression or mania in years, thanks to very good doctors and the right medications; I still have high and low periods, though. When I am depressed, seeing negative cards is especially difficult - on the other hand, though, when I'm manic, seeing all positive cards is just as bad. One problem I have with mania is that I feel like everything is terrific, I am terrific, I can do anything, etc., and having a negative card turn up reminds me that things are *not* always terrific, that I'm not totally fantastic and immune to anything bad ever happening again. Sometimes I need that sobering-up. Whereas getting the Sun or 10 of Cups during a mania would just reinforce my over-elation.
That said, using a deck that is all negative during mania or all positive during depression would not be beneficial either, I think. When my brain is giving me only one message, counteracting it with nothing but one message just reinforces the idea that the world is nothing but black and white, there's no "middle way" - and the middle is where I need to be. I have to feel, and accept, both good and bad.
Using a deck that encompasses both of those is therefore helpful to me, and especially doing spreads with a large number of cards, which usually means that there will be a balance of positive and negative. I've never done a 10-card spread that was all negative, for instance, when I draw that many cards some of them are bound to be more positive or neutral. I need balance, not simply cheering up or bringing down.
And I have to say that the most negative reading I ever had, with very few positive cards and the Devil and Tower in outcome positions, turned out to indicate one of the great turning points of my life. I faced the devil and the walls came tumbling down. I wasn't happy when I got those cards but in retrospect they were the most accurate reading ever, and their being negative cards actually indicated a positive result.
