Even Greener Pastures

We tend to use 'be taken ill' in fairly formal non-medicalcontexts e.g. 'Professor A has had to cancel her lecture at the Economics Institute because she has been taken ill'.  It suggests that no more information is going to be given about her condition. This is because it's not relevant, not appropriate or none of our business. We're in the realms of polite euphemisms - usually concerning the elderly - when we talk about people being taken ill.  You would never talk about a child being taken ill, and I can't imagine it being used for a young person (or by a young person).

I wouldn't use it in a pharmacy situation because it's not informative enough.'Taken ill' is fine if your job is to find a replacement lecturer, not if you need to prescribe medication. I'd go straight in and explain exactly what the problem is.