am I wrong for not texting back right away?

a couple of friends of mine are getting upset because I do not answer my texts right away for the past few months. it takes me days if the text does not require an immediate response. if it is an urgent thing and they need an answer right away, of course I would respond! but recently these past couple of months, I have been diagnosed with one chronic condition AND one chronic disease. I am young (in my late 20s) for both of these conditions/diseases. I have been experiencing weight loss, nausea and fatigue for two months amd going into my third month. I have gone to doctors appointments at least 7-8 times during these few months and have had 4 hospital visits for either procedures or examinations. on top of that, I still have to work and have church worship 2-3 times a week (which sometimes I can't attend because of my symptoms). one friend knows that I am sick, and is still frustrated that I don't text right away. the other friend found out two days ago and still is upset because I didn't respond to her latest text. am I wrong for not texting right away? I am not sure if I am in the wrong and being impolite, but also I physically can't do it