Yes, it does happen (indeed I've had to do it myself) but it is a very tedious process and can take some time. It will hold up in a tribunal if it is done right.
As other posters have said on here, it is quite possible that this could be a councelling discussion as opposed to a disciplinary one. 4 occassions of sick leave in a year is a lot, an employer has a responsibility under Health and Safety legislation to their employees so they may want to find out if it is something at work causing the issue. They may want to refer your friend to their doctor for example, if the issue is a recurring issue, they may want to know what the employee is doing to resolve the issue or to see if they can help in any way.