First of all, you should talk to your GP. When you are preparing to return to work after some weeks off sick, you may also need advice from your union rep, if available, or other independent adviser.
Involving your GP is very important. The GP will have knowledge of specific medical factors that need to be taken into account, which may limit your work activities, for a time or permanently. The GP will also be aware of any other treatment, e.g. physiotherapy that may still have to be completed. (See Dealing with Doctors.)
GPs may be contacted by an occupational health (OH) doctor or nurse for information, e.g. if you need specific help with your health in relation to work. Any information provided by a GP is subject to 'patient confidentiality' and to you giving your prior consent.
Rehabilitation means the process of getting yourself back to work, either to the same job or to an agreed alternative that is appropriate to your medical condition. It usually involves a return-to-work agreement (often in writing) between you and your employer.