Hi there, i shall try to answer your questions as much as i can, i have Bipolar so have first hand experiance of this illness.
First of all, bipolar is a chronic mental illness that is lifelong, but can be controlled and managed with meds and therapy, there is bipolar 1, 2 and 3 also known as cyclothmia. And through out there are 3 episodes, mania in severe cases milder known as hypomania, and then depression.
Your asking about the mixed state, mixed states are where depressive symptons and some symptons of mania persist together, this however is not being sad and happy at the same time, its all the depressive symptons like crying, no energy etc, but with the severe adgitation and irritbleness that occurs in mania, and impulsivness may come along aswell, this is known to be a bad mix as the impulsivness and the suicide thoughts, see how this may be a problem?
A person in this state would be depressed, feelings of hoplessness, helpfullness, guilt,. suicidal, crying, sleeping issues eating etc, but they would be really agressive, adgittated and be real irritated, they would maybe self harm, quite badly, not be able to sit down, anger snapping at people badly, punching things, this is how i am by the way, many people are different, Its quite horrible, i find myself feeling in a mixed state after a period of Mania, simply because after days/weeks being manic, you simply have taken all your energy out of your, i dont sleep at all or if i do very little, and im always doing somthing, yo yeah energy afterwards, i feel myself feeling really low, but i have that irritbleness and adgitation with it, i get severely stressed and angry at anything but yet i feel so dam low and depressed, its a horrible combination because depression alone is hell, but having that there too makes it ten times harder. This however does not last as long as my manics and certinaly depressive episodes.
You need any more information about Bipolar dont worry to mail me, i dont mind :)
Hope i helped. and if your worried about yourself, or somebody else, hope all goes well, dont leave it long it may become alot worse :) take care. xx