Is this the only time you have seen shaddows? What were you feeling when it happened? Prior, during, and after. This I found helps with understanding the nature of the visits. Again it all will be how you see them.
Like a paiting, everyone will have their own interpretation of what the artist was trying to express. Helps to keep notes on how you are feeling, what is happening, any key things such as smells, sounds, etc. It could be that we are lonely, or being visited by someone who has passed. Sometimes when I think about someone I lost, a few days later strange things start to happen. Othertimes the shaddows are just spirits moving around. Residue of another time playing out in front of me, or just passing through. But when those towering figures come around it is because I have done something I really shouldn't have.

These visits I dread. Like a child being scoulded. They do not have to say a word, I just KNOW. Why? Never found it in a book, it was something I noted dealing with what I am feeling inside at the time of the visits. Prior to the visit I can be in bliss, then the shaddow, boom I feel like a child again. I feel loved, but being corrected. I feel humbled. Then I go and relook at things that I have been doing to see where I have caused some problems, and try to correct it. But this is for me. What all those visits to you can mean something totally different. Just like a painting.
Since I do not see what you see. I cannot tell you my personal view of what you are seeing. It can be frustrating at times. Key is YOU, try to remember that. If you read it should mean this or that, but it doesn't feel right inside with you, then dismiss it. I've been seeing these things ever since I could remember. And I still have alot to learn.