Talk to the head of your course or your tutor. They will give you guidance on how to proceed.
They may also give you some paperwork to fill in. If you need to interrupt your studies for medical reasons, you will be required to provide evidence so that you are fit to resume your studies before you rejoin the course.
Interruption will initially be approved for a period of no longer than one year, and will normally be approved for a period not longer than a term/semester. You are entitled to apply for further successive periods of interruption if appropriate.
You also need to contact Student Finance England as soon as possible. This will minimise the risk of you being overpaid by Student finance.