This most probably isn't serious or anything to worry about. I've taken aspirin very occasionally in the past and then had an upset stomach. I never knew if it was coincidental or because of the aspirin so not really thought much of it.
However last night I took 2 aspirin tablets before bed. I was up nearly all night with bad stomach ache which has not yet gone. Along with this has been diarrhoea, although not bad.
Obviously I will avoid aspirin altogether now I know it's causing this. But is it something I need to go to the doctor about or do I just wait for pain to go and leave it at that?