Being neurodiverse as a physics student can be a highly varied experience, so the advice I give is tailored specifically to students with ADHD,and in particular, those who were undiagnosed when starting the course.

 The thing that took me the longest to realise was that I was not attempting the same course as my peers, despite the fact that we looked at all the same material and wrote in the same boxes in tests. Having undiagnosed ADHD is like walking with a ball and chain around your ankle, and then wondering why you cannot sprint like other people can. My best advice for you is to make your life as easy as possible because getting these adjustments is not ‘cheating’ - there is no pride in making your life harder when a mark you have acquired easily is the same grade as one you spent 3 all-nighters making happen.

 Acquiring an ADHD referral is as simple as booking a doctor's appointment and asking them to refer you, and that is all you need to gain all the resources physics has to offer. I was amazed that I could pick and choose from what allowances I thought could help me, and every lecturer I emailed was incredibly kind and understanding about extending my deadlines because my ADHD wouldn’t let me work until a few days before the due date. Communicating with fellow students can also be a blessing, allowing you to borrow someone's lecture notes after so you can avoid splitting your attention between note-taking and paying attention to the lecturer, and there are Physics Society events dedicated to the neurodiverse and their needs.

 In essence, the main advice I can give to you is to understand that your playing field is not as level as you once thought, and by asking for help in the department you can remove needless struggle from your university experience.