This may be the case for many people but I am sure my partner has Bipolar as his mood shifts are not a reaction to external circumstances but seemingly random. As someone with Bipolar I can recognise that he shows all the symptoms of at least hypomania (he May border on mania sometimes as he can lose all insight and grip on reality), and major depression, when he can barely get out of bed and feels utterly hopeless and extremely down. His episodes often swing from one to the other several times a day, but can also last more than a week.