Things you can do when you don’t have a lot of energy, but do have some time you need to get work done during:
Organize digital stuff.
Tag old photos, or make albums.
Organize your printed recipes.
Write draft replies for unanswered emails.
Create to-do lists per life/work/cleaning category.
Do short-medium-long term planning.
Work on time-consuming important, yet not urgent projects.
Make an inspiration board for the future – shopping lists, lists of movies to watch, books to read, places to visit.
Make a list of friends + plan when to call/interact with each one.
Crochet or cross stitch something small, yet meaningful.
Inventory stuff you have at home and/or plan on how to reorganize it.
Update your resume or explore jobs.
Do inventory of your health issues and make notes for future appointments.