This is a topic that I read about all of the time, do we cast if we aren't feeling 100%?
I think this is a personal thing, if you feel you can draw enough energy and focus it on what you are working on, and so long as you don't harm yourself in the process, then I don't see why not. You know yourself better than anybody else, you know what you are capable of and what your limits are.
For me having a chronic illness means it is highly unlikely that I am ever going to feel 100% OK. If I waited until I was absolutely fine then I would never cast anything, read cards, work for anyone etc. I would have yo give up my practice and this wouldn't suit me at all. From my own personal point of view, I know when I feel at my best for working and when I feel there is absolutely no way I will manage to summon up what is needed. Surprisingly the latter rarely happens.
I read somewhere that your energy can be toxic if you aren't well, but this doesn't feel like the truth to me. It feels like one of those long winded theories that have never actually been proven, or disproven. Again, I think you need to decide for yourself what you can and will have ago at and when is the best time for you, illness or not.
I have been thinking about this because recently I have been pretty well, but this past couple of weeks I have been having a flare up. I am not sleeping well - I haven't slept properly for a long time now - and I have that hit by a truck feeling almost all of the time, that feeling that someone has pulled the plug on my energy. If you have Fibro/CFS/ME etc you'll know what I mean, if you don't have this or know of anyone with one of these illnesses then the best explanation is that feeling you get when you have the flu. I'm talking the proper flu here, not a virus that lasts for a couple of days. If you have had the flu good and proper you'll know about it. You'll also know that achy, sore, lethargic feeling that you get, well that's kind of what the exhaustion associated with these chronic illnesses feels like, but only a 100 times worse.
Anyway, I'm getting good at knowing my triggers and knowing when stress is going to factor in my life. I'm getting good at having the kind of lifestyle where I have to spend oodles of time resting, or sleeping, or just feeling meh. I am getting awesome at working around this illness and know when I have enough energy to work magick. I think that my results prove my energy isn't toxic and that I am working well.
I think we need to concentrate on our own energies and focus, we need to trust our own judgement in these matters.