In reply to Pesda potato:
It's an interesting question. I bruised my ribs at the beginning of the year. It was extremely painful to climb with even climbing 6 grades below my normal level. One time I took paracetamol and ibuprofen and could climb almost as well as normal. But I worried that I might be making it worse so I only did it the once. After that I continued climbing unmedicated at a low level and to my surprise it was pretty much healed after only 3 weeks.
I suppose the test is if you climb with anti inflammatories whether the injury feels worse later when they've worn off. Immediately after it might well feel worse but maybe 6 -12 hours how does it feel? Or a few days, will it be still getting better or have you re-injured it by climbing? Certainly for the first session or so take it easy to test it out.
I'd take it as a positive thing that injury was not caused by climbing. To me that suggests that it won't necessarily be made worse by climbing.
Sprain's can vary from mild to severe. I sprained my ankle months ago and its still not right yet. Fortunately its not affecting my climbing, aside from jumping onto hard landings.