I think this is very common, almost inevitable. Perhaps it's more apparent in the case of specific or individual trauma, but even for those with a complex history of ongoing trauma, there are usually key events or turning points which take on the status of anniversaries.
In my own recent experience, it doesn't matter whether or not you're prepared for it or if you school yourself to try to believe it's no big deal, it does still impact significantly for many of us.
All you can really do is make sure you've called on all of your support network to gather most closely around you at this time, are using all of your coping and management strategies as effectively as possible and have taken steps to remove as many unnecessary stressors from your life as you can - you don't need any extra issues to be dealing with at this time.
I'm sorry that this looms ahead of you. Keep us posted, maybe it will help to talk/journal your way through this difficult time a little.
Maddog
