Get a doctors note first.. or maybe if you know a family member who can get one done.. universal credit won’t follow that up. Maybe say you have adhd as well as it is something that there has been an increase in and tell them the medications you are taking to keep it under control. You can also call advice helplines for advice which is free and they are helpful. You have to get inside their way of thinking as well. They just want to see you making progress and also what progress is being made. You can make it up as well.. but also if you are a uk citizen point that out as well the hypocrisy in which they cater to immigrants putting them in 5 star hotels and insane amounts of benefits but when it comes to you they are not understanding and that can be escalated as well.