Hi Lilackez
It's common for claimants to have their first interview with JCP before the decision is made. The following interviews are usually with a private sector organization and take place after the decision.
From my experience and many other members experiences, the first interview with JCP is an ordeal, or comical, depending on how serious you are.
They try to encourage you by convincing you that your disability is minor and will get better soon, and that lots of companies will be falling over themselves to take you on. You can expect the following interviews to be a lot more realistic, as a private sector company would be wasting their own money placing a client on a scheme that was not suitable.
It's important that you attend the interview and participate for your ESA payments to continue, but I wouldn't be overly concerned. It's unlikely that they would expect you to do anything before the result of the medical.
Good luck
Derek