Does anyone have a problem with their brain blocking out deep thought and prolonged reasoning?

For awhile now it seems like my brain blocks out prolonged reasoning and deep thought like when I'm trying to really go into deep thought and focus on something. I used to be able to use pictures and scenarios in my head that would help me learn now whenever I try to do that my brain blocks it and I begin to get anxiety and depression from this. Also I have sometimes uncontrollable thoughts that can sometimes overtake my functioning in life. Please help if anybody has this same problem. Tips if any?