Hi,
for me the mixed episodes are definitely the most horrible and I have had many in my life. After being diagnozed with bipolar I had a few during the first months when we tried different medications, but also had one last summer when there were no medication changes (and it lasted over a month!). At least for me the episodes (regradless of whether mixed, depression or hypomania) are usually caused by some small and sudden change in my life, as was this mixed episode last summer. Although, sometimes I think episodes can be triggered by just about anything.
Having routines in life probably helps, because if something sudden happens, being stressed or physically exhausted can be the thing to push you overboard.
I hope you are doing better, and that you will never get another one in your life