i've been lurking this forum for a long time now, but somehow felt compelled to finally register and reply to this post.
well, it looks like your sleep paralysis is developing to include the elements of hypnagogic hallucinations. at least, that's how it was for me. for the first year or so of having SP, i would get only the sleep paralysis itself. today, few years later, my hypnagogic hallucinations are now severe to the point that they are now visual, auditory, and tactile. also, i can get up to three false awakenings in a single dream. this means that multiple times in the same night of sleep, i can DREAM that i'm having sleep paralysis and get all the same characteristics, shake myself out, and still be in the dream; then it can happen again later on. however, i still have not experienced any astral projections, OBE, bilocation/doppleganger, or anything else of that sort, though i have been expecting it lately to be able to happen at any time, since my condition hasn't further developed for a while.
as for the sense of impending doom, it is a prevalent characteristic of the hypnagogic hallucinations, and i have always shook myself out of them. i've tried to sit through them, but nothing really changes. the feeling of danger and the silhouette that i see just remain until i crack and finally decide to shake myself out.
there used to be a VERY good, and VERY informative page on it on wikipedia, but some idiot (imo) deleted it and made the term "hypnagogic hallucinations" redirect to the Hypnagogia page. repeatedly reading through that old wikipedia page and lurking this forum has helped me cope and relax, knowing that it was a real condition that many others experience. i guess you can probably find information about it with a google search. as for "letting" it continue, i don't have any idea how you can prevent it from occurring. it's something that's always happened to me, and has always been getting worse over time.
edit:
i don't mean to mislead or misinform you. and, depending on how new you are to reading up on sleep paralysis, my post looks potentially fear-striking, which i also did not mean to do. out-of-body experiences are probably not necessarily a "severe" form of the condition, and it might not be typical for conditions to gradually develop and worsen over time. it is, however, how it has happened in my case. anyway, i am mainly trying to say that from what i would deduce, you are not currently experiencing anything along the lines of an out-of-body experience, but hypnagogic hallucinations, while, at the same time, sharing my own experiences with the readers on this forum, because the more detailed posts from people that i read personally, the more comforting it is to me. also, i am not an expert on this subject; just a long-time sufferer.