Redirect yourself. Put all law-related stuff out of your sight, take the Biochemistry book in your hands, and look at it.
It might take an hour for you to open it. Keep looking at it, you will open it eventually.
Thenk, start reading it where you're supposed to read. Taking notes, especially on the computer if handwriting is challenging, should help you focus on the reading.
After a while, you might find yourself drawn into it. If you don't, just look away, take a deep breath, and then try focusing on reading the textbook again.
Also, if you have other things to do for this class (e.g. papers), make a plan for them first. Think what you want to do first, second, third, assign time to them, and work through each thing one by one. Putting a timer for a number of hours you plan to work will help you focus.
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Leading a double life and loving it (but exhausted).
Likely ADHD instead of what I've been diagnosed with before.