Mourning the death of a loved one is difficult, and it can take a long time before you move on, but you will be able to move on. Most advice will tell you that “moving on” is more of a metaphorical goal. You have to get past the bereavement period in your own head. While this is certainly true, it’s wrong to think that moving on cannot also be a physical way to cope.
What keeps you in a state of brain fog is your thoughts that take up space in your mind. If you could look into your mind, it probably would resemble a cobweb - one thought inter-twined with another, connected to another. Who would feel clear with all of that going on? The more you think about what to do, where to step, what direction to take, the less clear you become.