I've got freshers flu (well, not flu, but freshers cold doesn't alitierate as well) atm, but I once did a gig when I had flu AND a put out back, at the time it was our biggest ever gig and I really didn't wanna let the band down, luckily the stage was next to the doors for the beer garden so I laid down outside and threw up probably more often than I hit a string, but I made it through, probably set my recovery back on both fronts 2 weeks, but it was worth it
Like someone else said, scotch is a very good cold cure, alcohol numbs the sore throat and constricts blood vessels so it helps the blocked nose, and I'm pretty sure lemsip doesn't have a distinctive islay smokey finish accompanied by a warm feeling of inflated self confidence.