Why is it that when my depression lifts, my anxiety goes sky high?

I am seeing a pattern...

Depression lifts to reveal paranoia and anxiety for several weeks, then I get all hypomanic and have all sorts of revelations, only to drop back down, feel vulnerable and drop back into depression.

I know Lithium is doing something, because I have been able to exercise and feel a little less overwhelmed with life this week.

Is this as good as it gets?