If you're hallucinating, you need to call your doctor and tell them you're having a bad side effect. You're probably going to have to try something else--Lexapro is obviously not working the way it should.
Don't worry too hard about it, though. I've had hallucinations, once, when I had a high fever; it didn't damage my brain or anything. It was just annoying and disorienting. Just don't take the next dose, and call the doctor ASAP.
With Christmas coming up so soon, the doctor may be out of the office, but you probably have an emergency nurse line you can call for advice, or an emergency psych hotline. Try them. This isn't precisely an emergency, since you are experiencing only minor hallucinations that you're very well aware aren't real, but it's still not something you want to have to deal with for too long. Nobody will be upset with you if you call in about this problem. Besides, the sooner you get a doctor's appointment, the sooner you can try a medication that might actually work for you without making you see and hear things.
Vivid dreams are a common side effect of many medications. If you're still sleeping well, they're not a concern. If they wake you up and you can't get back to sleep, that's probably something to ask your doctor about, since getting a reasonable amount of sleep is one of the things that helps speed recovery from mental illness.
I have very vivid dreams, and remember most of them. Unfortunately, many of them are repetitive nightmares. From this experience, though, I can tell you that it is entirely possible to get used to it, learn to go back to sleep, and generally have it not affect your quality of life. There's this theory that dreams are your brain practicing for really bad stuff--like, if you're being chased by something horrible or beaten up by somebody, or whatever, that's your brain trying to learn how to react if you are ever in that situation for real. The idea is that our ancestors couldn't really practice getting away from sabretoothed tigers without getting themselves into some serious risk--so their brains learned how to "practice" at night. Don't know if that helps you any, but it does explain a little about why people might have nightmares like that. It's not just your brain trying to torture you for no good reason; it's because there's a problem you're trying to solve.