Congratulations! My two kids are 23 months apart, so I can't give you any first hand knowledge, but I have had quite a few friends that have small gaps (one is 13 months difference) - most have been planned, one was a breastfeeding accident.
Think of the positives....your kids will be close in age, and probably very close friends too! The experience will be fresh in your memory, so you'll remember much faster what works in a situation and what doesn't.
You'll be fine. If my friends can do it, you can too!
P.S think of it this way....you may have a longer time of interrupted sleep, but at least you'll be able to get it over and done with....(It's much harder when you've gotten used to sleep and then it is 'taken away" again!)