I do experience hypnagogia sometimes. I dream very rarely though (a couple times a year, maybe).

If I really stretch the definition of "imagery" I can sort of invoke the feeling that I'm seeing something, but your description of visualization is way too vivid to match that. I literally can't imagine it :P I can't really hear things either unless it's a very recent experience, and even then it's more like the "feeling" of hearing something rather than anything really auditory.

The note about prayer is interesting, but I've been non-religious my entire life and I've never uttered a prayer with any sincerity.

If you asked me to describe my family to you, I probably couldn't do so with any sort of accuracy. I could probably tell you their most recent hair colour and maybe some very generic features, but I can't recall for example anyone's eye colour besides my own.

I gave a shot at trying to learn to draw at some point, and made some progress towards being able to replicate what I see, but drawing always seemed to be a process of trial and error, since I'd have no idea what my marks would end up looking like before I put them on paper. I did enjoy it when I really got into the drawing process, but the good parts weren't really good enough to outweigh the massive stress and frustration it usually caused.