I came across some information on the internet (of course, right?) and discovered that the calendar I've had in my head my whole life is apparently not something I share with everyone else in the world, like I had previously thought.
Ever since I was little, I have always had this calendar (illustrated below in my not so great drawing) and every date has a spot. If someone says May 8th, there's a specific spot for that. If someone talks about a wedding on a specific date, I automatically "zoom" to that spot in my calendar. I can't picture doing it another way and I can't not think of the calendar.
I was amazed when I came across a thread of people talking about this calendar and some of theirs go counterclockwise just like mine. You will note that December is the only thing on top and the summer months are all together on the bottom. It's almost like a clock, but not quite. July "belongs" at the 6:00 spot because it's the middle summer month, yet December still belongs at the 12:00 spot. The "inside" is just hollow, by the way.
I also have an amazing memory. Not only can I recall many, many childhood events (I remember one time having my diaper changed and I was in the hallway between the two bedrooms; another time I was in my crib and I could hear my pulse when I was on my side so my mom came in and sang "Tomorrow, Tomorrow" to me), but my sister and I can both remember specific days: what day of the week it was, what the weather was like, what we were eating, etc.
I can remember birthdays, phone numbers, and for some reason the employee numbers at work (I do work in HR, but still, I don't try to memorize the 4-5 digit numbers, it just happens). I associate these numbers with faces. For instance, my friend, C. Her birthday is May 8th. Every time I see or think about her, my mind tells me "May 8" but it's not like it takes over my mind -- it's just there. I can remember that my 7th grade locker combination for the top and bottom lockers: 42-14-40 and 9-39-11. It won't probably ever go away. It's stupid trivial stuff! When I was in school, I could study by staring at my notes and I would memorize them and when I was taking my test, I could see the notes: the style of writing, when it got to a new page, etc. in my head. I could also memorize sheet music the same way: I would see when it got to the end of the line and to the top of another page. I mentioned my sister. She can also remember birthdays and phone numbers, but she also has another type of synesthesia: grapheme, or color synesthesia. Every number or letter for her is a certain color and it's been this way since childhood for her. She doesn't "get" my calendar and I don't have a color/number association.
Synesthesia is more common in women than men and it can be hereditary. There aren't any documented cases of men passing along the trait to their boys, so it is thought to be "X" linked.
More about Synesthesia from Wikipedia. If you click on the link, you will see that it is involuntary and thought to affect 1 out of 23 people (so not too terribly uncommon, but it's not like everyone has it either).
I also found some blog posts on Synesthesia. Here's the one that me going, "OMG, I am not the only one with a calendar in my head?": Link and another: Link
Anyway, I think it's cool!