You have to pick:

You are not allowed to urinate until the injection is complete (though you can immediately after).

You have the symptoms of the cold, but you're not contagious. Also I would suggest that cold symptoms are that awful sick feeling, achiness, sore throat, and runny nose. I don't think it would include vomiting, diarrhea, rash or any other symptoms associated with flu or more serious diseases.

You CAN medicate, but its one of those colds that is so bad that you still feel wretched after medication.

According to http://hypertextbook.com/facts/2001/DanielShaw.shtml 1 liter is at the very upper limit of the usual range of capacity for the human bladder, so most people aren't going to be able to hold that much and will risk rupture. Could be quite serious, and wouldn't be surprised if it'd lead to kidney damage and infection.