I agree with monitoring more frequently just to be sure. I take a Lantus dose at around 9 pm and lost count of how many times I was startled awake, desperate, wondering if I had taken the dose that night. I recently started changing the pen's placement everytime I take the shot, replacing it when I do the morning fingerprick test. Now, if I wake up in the middle of the night, I can look at where the pen is. Even then, if I suspect I forgot to take it, and can't know if I either forgot the dose or just forgot to replace the pen, I consider the possible scenarios:
-I took the dose, don't remember, and take another one (to be "sure") and risk a terrible hypo while asleep and further hypos through the day;
-I didn't take the dose, and then take a full dose (nothing happens);
-I took the dose, don't remember, and leave it (nothing happens);
-I didn't take the dose, leave it that way and risk high blood sugars the next day (which can be remedied by a tighter control).
The first case is the worst one, by far, and I'd rather risk high sugars (when that happened to me, it was not that bad) and having to correct them, so, if I suspect I didn't take the dose, I just ignore it. It is a hassle, yes, but I think is far safer.
In any case, I second the opinion of contacting a professional when in doubt.