I too carry medication: rehydration salts, antihistermines, pain relief etc etc. I also try to drink lots of water. Much more than normal.
I have only felit too ill to curtail activities twice I think (both through a dicky stomach) and then I chose as a precaution not to go out on a game drive or a walk. I did not want to risk carrying on as normal and then being ill for a much longer period. Miss a morning or miss a few days?
The only time when I really should have missed game drives was a couple of years ago in the Mara.
We had been travellling for ages trying to find a safe lunch spot therefore when we finally stopped I hopped out the car to help my guide hoping this would speed things up. I duely noted that the back of the vehicle was open and was being ultra careful not to bang my head that i forgot to also look where I was walking and fell into a small hole in the ground. Alternative version: I was in the Mara enjoying lunch when a buffalo suddenly appeared and charged us. Wanting to save myself I ran to the vehicle and launched into a flying leap to get into it. I fell badly on landing.**
There was a tremendous crack and for about 30 seconds I thought I had broken an ankle. As I wasn't rolling around on the floor in agony I pretty soon realised that nothing was broken. My guide I have to say wasn't very much help. I used the cool box and the seat to elevate my foot and we eventually got back to camp. Via the Mara River where my guide actually stopped and asked if I wanted to walk down and see the crocs...croc vs guest with a damaged ankle...what are the odds My guide suggesting along the way that the solution was to put 'deep heat' on my ankle when I got back to camp!
Luckily a manager was present who had done paramedic training and he looked at my ankle and with the usual I am not a doctor caveats confirmed it wasnt broken but sprained. He very quickly arranged to have me helped back to my tent and there I sat with my ankle in an ice bath for the nexct couple of hours or so. Then this got changed to cold bandages/towels which remained on during the rest of my stay. The camp bought dinner to my tent that evening so I didn't have to walk to the mess tent. The next morning it was a test to see if I could walk but luckily I could so with a lot of help I hobbled to my vehicle and with my foot still elevated and bandaged and cold I went out on a game drive. I did the same in the afternoon. My logic was that there was no real difference between sitting in my tent or a game vehicle so the game vehicle won out!
The next morning I was leaving for Nairobi so the land agent arranged for my driver to take me to the hospital for an x-ray to confirm nothing was broken.
6 months of physio later (yes I had naturally a severe sprain!) my ankle was almost back to normal.
** An alternative and a much more interesting and thrilling version but unfortunately not true