I can't imagine anything - I do everything from memory

I have always really struggled to imagine anything. Like in therapy for example or other types of healing, they say to 'imagine a white warm light beaming down on you' or something like that. But I literally cannot do that no matter how I try. The way I 'imagine' things is by recalling it from my visual memory. So if someone says 'imagine a tree' - I cannot just imagine a tree and conjure up this image from nowhere. My brain automatically goes through the filling cabinet of memories in my mind and says 'tree, tree,tree, where was the last time I saw a tree?' then I remember I saw a tree in the park on a walk 2 days ago so I then bring that exact tree to my mind from my memory. 

But this is difficult when people say to imagine something that I have not experienced before or does not exist. I don't know how to create these made up images in my mind. Does anyone else understand what I mean? 

I think it's also one of many reasons why I struggle so much to imagine the future or something that hasn't happened yet as to me in my brain I cannot imagine something that is not already in my memory. I don't know if I am making any sense but I feel so alone. 

The more time I spend with other people, the more utterly disconnected I feel from everyone else around me. I feel more lonely and more alone the more I spend time with others. It just feels like no one is like me.