I've been doing tarot for years, haven't sensed anything untoward. I personally feel light and dark are inside us, sometimes projected out. If you approach tarot objectively, ground yourself in the way that is best for you (eg, meditation, walks, ect) and do it in moderation, you'll be fine.
In pondering, the images in the cards may trigger your own unconscious, which may show you lessons for you to work through - a self-exploration journey which may be easy or hard. That's the only thing I can think of that the tarot has triggered for me over the years. No strange astral phenomenoms....
NR