I saw a few other stories on this site regarding visions, so I thought I'd share my own.
All of these visions occurred while I was fully awake. I don't do any drugs or drink.
The first one I'd like to describe occurred while I was listening to a religious audio dictation. I was lying in bed, listening to the audio, not really paying attention to what I was perceiving with my eyes.
The audio lecture was a recording, so it should be a unchanging audio, but it was connected to the internet, so it is possible that a cyberattack was involved. As I was listening to the audio, the dictator said "God will show you what it looks like" (using a foreign language). Immediately upon hearing this sentence the vision occurred. I've checked the audio recording, and it doesn't contain that sentence.
Anyway, the vision occurred really fast and totally consumed my entire visual field. The vision was perfectly crystal clear, I was surprised how clear it was because I don't have good eyesight and I constantly misplace my glasses, so usually what I see it a bit blurry.
Anyway, it was dark in my vision, and I saw a enormous black spider, taking up my entire field of vision. I am not certain that it was a spider, because it's legs were really thick and strong, almost reminding me of a horse. It definitely had more than four legs though, probably eight and perhaps ten.
Anyway, the spider was charging at full gallop, almost like a horse at full speed. I was calm during the vision, and it only lasted for about five seconds, but the spider-like thing that I saw was utterly terrifying, probably the scariest thing I've ever seen, including the imagery in the movies.
After the vision, my room returned and I felt fine, perfectly alert.
Another vision that I had occurred while I was lying in bed, although I was wide awake.
Again, my entire visual field, including my peripheral vision was totally replaced by the vision. In this case, I perceived that what I was seeing was South America in real-time, and what I saw was a jungle scene, everything crystal clear, with two male South American children in the center of my field of view.
The children were really happy and were hugging each other and smiling and waving their hands in the air. I perceived that they were aware that I could see them, and were happy to see me, and were waving to me personally.
The vision only lasted for about five seconds, but again, I was surprised by the clarity of the image and that it totally replaced my entire field of vision. After the vision ended, my perception of the room I was actually in returned.