Do I need a sickness certificate from the doctor?

You only need a sickness certificate (also known as a sick note, med3 or fit note) if your illness lasts more than seven days.

You can complete a "self certificate" if you are off work for up to seven days. You can download the self certificate form by following the below link;

https://www.gov.uk/taking-sick-leave

Do I need a "return to work" note?

No. You do not need to see a GP again to be signed fit to go back to work.

The fit note does not have an option to say that you're fit for work. If a doctor wants to assess your fitness for work again, they will say this on your fit note.

Some employers have their own policy that requires employees to obtain medical evidence that they are fit for work. If this is the case, your employer should help you arrange this privately with a GP or occupational health specialist. A doctor cannot issue a fit note for this purpose.

https://www.nhs.uk/common-health-questions/caring-carers-and-long-term-conditions/can-i-go-back-to-work-before-the-end-date-on-my-fit-note/

Obtaining a sickness certificate from hospital..

If you are off work for more than seven days for an illness that has been treated in hospital (including A&E), you should obtain a sickness certificate from the hospital Doctor responsible for your care.