It's also good to realize that as a kid gets older their world expands exponentially, and so do the things they fear. At 13 months old, your son is now old enough to have disturbing dreams that are far more emotionally complicated than "falling" or "being scared".
That said, you could also have a kid like mine: at 13 months old he cracked his first joke, saying "umbrella" when my mother told him to stop blowing raspberries on her. I get the bragging rights to things like that, but I trade off in things like sleepwalking/talking and night terrors. He is simply capable of intellectually absorbing more information than he is emotionally capable of dealing with.
Pay attention to what specifically happens during these episodes. Does he ask for anything? Try to leave the bed? Make any demands upon you? There is a difference between a kid who gets up and wants a bottle and a kid who wakes up scared/overwhelmed. But keep in mind that these differences are for your edification only: in either case the solution is to quietly and without fuss lay the kid back down without doing anything which would subtly or overtly encourage the behaviour.
It is normal for children to awake somewhat during the night, and normally they simply resume their sleep. However, if they are uncomfortable for any reason (e.g., 'expecting' to find a pacifier, wanting to be held, wanting a bottle) they will cry. The matter is complicated by having him sleep in your bed. My best guidance for you is to have him sleep in his own crib, and for him to fall asleep each night without you holding him and without items such as pacifier, bottle, etc. He will learn to fall asleep on his own and to resume sleep if he does wake up. You will have to bite the bullet, though, and let him cry it out. If you persevere, he'll be OK. Take a look at Richard Ferber's book titled Solve Your Child's Sleep Problem fora useful and detailed discussion of pediatric sleep issues. By the way, if this has occurred suddenly, be sure to have him checked medically. Ear infections, e.g., can be accompanied by such behavior, and eventually teething can bring nighttime discomfort.