Rest.. proper rest. Sitting down and actively resting
Sleep. The best sleep you can manage. If not, then more rest.
Planning and doing a few jobs to make your surroundings nicer... wipe down the kitchen, put some washing away, tidy the hallway, brush up outside the front door.
Doing something trivial but mentally distracting e.g. word searches or reading a light novel
Being outdoors... in a peaceful a place as possible... Garden, park, wherever.
When you feel more energetic, commit some thinking time to identifying why you feel the way you do. And then working out what your options are to address it. This can take weeks.
Really really taking time to notice the good things... a bird singing, the smell of a honeysuckle as you walk past, a pretty soap bubble, two strangers sharing a hug. Tell yourself how lucky you are to witness these things, how you would have missed them if you'd not gone outside.
If you're worn down by people, remind yourself that this is really being alive... if you're caring for others, you really are at the heady heights of the good things that humans do.
Eat some fruit and vegetables, drink water, avoid caffeine and alcohol.
Make peace with being a human being, not a human doing.