Thanks, Anne. Mine and M's friendship actually does have a history of spontaneity - agreeing to accompany me to a concert or a movie only hours beforehand, for instance - so I wasn't too concerned about that...although maybe next time, I'll try planning a bit more in advance.
I found your post useful, thanks
And I did go ahead and call her last night. She didn't pick up, but I left a casual message for her...no yearnings or loveydovey stuff...just the same as I'd always sound. I'm going to let it rest with her now, and wait for her to get back to me before contacting her again. If she's uncomfortable to any degree, I'm certainly not wanting to push it.
I do fully agree with your suggestion for the next date, when/if that happens. I had no plans of turning things up, but simply hanging out in the same manner that we usually do...and if something happens, awesome.