I'm wondering if mental illness is carried over into the space between lives and then subsequently to the next birth?
Wrong view can cause long repetition of bad existences, yes. So look always to straighten right view. to learn about what is right view and to stop ponder around about kamma, since such is one cause of getting "crazy". Beest right here and now!
(Its not given for your trades, stacks and to maintain exchanges, but as a tiny emergency exit out of the wheel you are, in if wishing so.)