You must remember that while there are many people that have been educated in tolerance and are able to see others’ conditions without making assumptions about their character, it is true that there are also too many others that have refused to or did not have the chance to learn it. Therefore, not everyone is able to understand words such as “ill”, “trauma” and “health scare”, and think those can be indeed debilitating (and last for more than a weekend), and not the case of a kid that doesn’t want to get out of bed to go to school in the morning. These people are also probably the ones who did use fake “sick” excuses to not go to class and go play elsewhere. Even if you didn’t use such excuses, and knowing that it may be misinterpreted, you must be aware that some people will understand your silence as aggression because of such ideas, and this does not depend on age.
Such situation makes any person uneasy about others’ thoughts, especially if it is a colleague. However, just because your colleague does not understand, it doesn’t mean you have to sacrifice your path to well-being and go back to ground zero, change your priorities to meet their – likely arbitrary – deadline. You know you will do what you have committed to, but you should not do that at the expense of your own capacity: do not keep forcing a piece of broken equipment to be used until it is completely useless; do not ignore cracks at the foundation. However, always keep the resolution that even if your limits are low, you must try to reach them, and not give up; reaching and expanding them is the only way you can see if you are improving.
As such person is unable to understand illness as a cause for not working on the project they want you to prioritize (which you must question, if you have indeed committed to give such priority), it will be only to your disadvantage to show yourself or your work at any of the “recovery” stages, that is. A friend may understand a bad appearance, such colleague won’t. Yes, a lack of certain kinds of vanity is tolerable and even praised in certain work environments, but you will find that this is not as common. Some colleagues may be able to follow your reasoning in an experiment you haven’t finished, but not such colleague. Therefore, calm down, and keep on, for your best results, and not for fear or uneasiness caused by others.