These are common hallucinations seen just before sleep, somewhat like pre-dreams, but you are still fully awake. Approx. 37% of people have them and they vary from simple patterns or shapes to full dream-like scenes and movies, nearly always surreal and unexpected images. There is an interesting Wikipedia article here. 

My experience is that I have these every night before sleep. They sometimes start with brief patterns but quickly, frequently immediately, become images or short movies that morph from one image or scene to another in a few seconds - I usually have about 5-10 seconds per image or movie before it changes into another. They are surprisingly random and nearly always unique and a bizarre combination of objects. My experience is I can both see the image itself and the blackness of my closed eyes at the same time, but the image is much more captivating, so it dominates over the darkness. I enjoy watching them and usually they lead to me being asleep in a few minutes, although one night I spent over an hour watching them like a surreal movie. Sometimes they are very intricate (like lots of gold filigree) often moving and almost impossible for me to draw. I found an interesting simulation of what people see on DMT and some of the later stages are much like my more complex hypnagogia. e.g. see this video which gives a good simulation of the frequent complexity of the images and way they often move. Sometimes you may move through a scene, such as floating a few feet above a forest of tree stumps in the rain, most of the movement is fluid like the video and morphs from scene to scene. I was struck by how the judder matches what I've occasionally seen just like the creature towards the end of the video. I've never take DMT or any hallucinatory drug, so it's intriguing the hypnagogic experience is so similar to that simulation, it must surely tell something about how the brain works.

There are equivalent and very similar experiences on waking called hypnopompic images. I have those occasionally and though very similar they tend to be shorter and less engaging. A few of these images below are hypnopompic - I've noted in the captions when they are.

I also have occasional auditory hypnagogic phrases that I hear usually when drowsy during the day. I can sometimes catch them and write them down. They have a similar surreal quality to hypnagogic images in that they are an unusual and very novel short sentences, rarely making sense, but sometimes amusing, like their image counterparts. They are occasionally poetic like "he gave me thirsty colours", paradoxical like "(Whispered) this can only be helpful if one of us doesn't believe it" or maybe something that could have easily been one of the images below such as "Yellow gorilla standing on a rolling pin". It seems the brain is up to similar things, whether visual or auditory. I have a separate page on hypnagogic phrases.