I started taking K2 (5mg) over a year ago. I started taking it at night, but moved it to the afternoon because my mouth started falling open as I slept, which makes for an awfully dry mouth in the morning. So, I kept moving the time I took it- I took it in the afternoon for a while, and then recently started taking it in the morning. Now I've skipped a day and I guess two, because I didn't take it this morning and certainly don't want to take it in the P.M.
Even this annoyance is actually a benefit- I used to grind my teeth, but I don't anymore.
With some Googling you will find articles on whether there is a K2 upper limit. From memory, no significant side effects were found at levels of 45 mg/day. I don't remember how long that dosage was maintained in the study.
I'm skeptical the K2 is causing you to sleep with your mouth open. I also wonder how much you were absorbing if you were taking it at night, unless you were eating some food with fat at the same time.