Just wanted to add my best wishes & to agree with many of the comments above.
Dove's suggestion to contact Macmillan is an excellent one. Similarly, many towns now have a local Volunteer Centre and they often have a list of people who would be pleased to help you look after your lovely garden - either short term or long term.
On a practical level - if you (or somebody) is able to manage the lawn, I think I'd keep it (or most of it) - a neatly edged & mown lawn can detract from a multitude of sins elsewhere!
The suggestion to significantly reduce the number of pots is a good one as they are really quite labour intensive and unforgiving if neglected for more than a couple of days in hot weather. I would also consider planting a lot of low maintenance shrubs in the borders (things that require a once a year tidy up rather than regular dead heading) - viburnums, eleagnus, cotinus spring readily to mind. Some good ground cover plants in between will help cut down on weeding.
If you are still able to be out and about pottering you can still have a couple of small areas to do the jobs you really enjoy doing - perhaps a couple of patches to sow some annuals each year for a bit of colour allowing you to keep your hand in with some light dead heading - especially if you can do it whilst sitting down.
Good luck with your treatment and - as others have said - give us an idea of where you are & you might have a small team of new friends turning up - trowel in hand