If you are tired, it is best not to try to ap. It is a good idea to get some sleep first and then ap if you are tired. If you are not tired, it will not hurt trying.
When I have been trying to ap when I just go to bed, I want to ap but a part of me does not want to. I try and try but it does not work. It probably sounds strange but I keep fighting with myself. To solve the problem, I have been saying to myself I can ap in bed. I want to ap in bed. It has worked. I have not ap but I have made a big effort in trying. I will keep persevering with it.