answered Sep 11, 2010 at 11:25PM
Ibuprofen is acidic in nature. As with all acidic compounds, it is general practice/advice to tell individuals to remain upright (not necessarily standing, but at the least sitting up) anywhere from 15 to 2 hours after consumption, depending on how it affects them.
But I agree with Gina - the risk of choking or regurgitation is greater if an individual lies down straight away - particularly in those medications which have been proven to cause GI upset