If you're wearing an activity tracker, seeing a lower calorie burn due to injury or illness can cause a kind of panic where you feel like you're not burning as many calories and therefore shouldn't eat as much food. Thank you, diet brain.
No worries, your appetite doesn't lie to you. Diet math does. ALL the time. Because I see the numbers on my Fitbit but I eat according to appetite, the mismatch becomes super apparent. I may be very hungry on very inactive days or vice versa. Even if you're sick or injured, there may be a lot going on metabolically with healing and recovery.
It's important to give yourself full permission to eat whatever, whenever, and as much as you want. Empower yourself to make choices. That mindset brings peace around food. "Ok, I can eat it all and then some. Do I even want to? Would that feel good?" Sometimes yes and sometimes no. If you eat more now, you'll be less hungry later. That's all. Nothing dire. The important thing is reminding yourself that you're free to choose and it's not possible to choose wrong. You'll learn something either way. "I can't. I shouldn't. I have to." thoughts are so scary and disempowering. Total diet noise. If those come up, swat them like flies, especially if they come attached to a number. There is a vast mindset and outcome difference between, "I don't want that right now. I'm full. Maybe later" and "I can't have that. I didn't exercise enough. I must cut back and go hungry."
When injured or sick, go ahead and eat what you always eat. Include everything you want. See how it feels. It may pretty quickly feel like too much food. No problem, because you can make adjustments for maximum satisfaction. Maybe you still eat big meals or extra desserts sometimes, but find yourself a bit less hungry for the usual kind of boring food. That's what you cut back on if you're feeling too full, ok food that you're not particularly hungry for, not the good stuff.
I find that when I'm sick, injured, or just taking time off, I eat basically the same as always. My portions of some things may get smaller because I'm not as hungry or lose interest sooner, like with my cereal bowl, sandwich bread, or steak size. But some things will be the same, like chocolate, pizza, dinner with friends. There is no desire to reduce those, so they are not reduced, but I don't want the whole mountain of mashed potatoes or the second pork chop right now. "Not now, maybe later" is a helpful phrase. If you choose to eat a bit less of something right now because you're full or not that into it, remind yourself that eating it later is always an option. If I focus on that freedom of choice, I can easily eat to appetite. If I "shouldn't" have something, I want it!! All of it! Now! It's funny how that works.
Here's another really important concept: I'm eating to the same levels of fullness and satisfaction regardless of activity level. If I've been considerably less active for awhile, it might take less food to get there, but I'm no less satisfied. I'm not stopping short of totally satisfied and wishing I could have more. That's restriction, which results in feelings of deprivation and eventual overeating. It doesn't become necessary to restrict when your activity level is lower (or for any reason). Your appetite will naturally follow whatever your body is doing. It's just a matter of getting your brain out of the way if it wants to "implement strategies" instead of letting your body regulate according to its real needs.