When a co-worker wants to be an informer...?

If an employee stays home sick and calls in sick, do co-workers have the right to question your validity or should this be an employer/sick employee issue.

This happened to me at work a few months ago. While I was actually sick, this became a topic between my boss and another co-worker who took it upon herself to ask me. When I suggested the boss had perhaps put her up to this conversation, she denied. Less than 20 min later my boss came up to me and said in front of everyone else - so you really were sick.

While this co-worker and I had (or at least I thought we had) a good relationship prior to this, she now acts as if nothing was done wrong I find myself wanting to protect myself and privatize.

I suppose a workplace might justify the lie for the end result, but I feel it also makes for low moral among co-workers.

I haven't confronted the co-worker....wonder if I should or should I just keep my distance for a while... let her fall into her own lie somewhere else. At the time I felt I shouldn't confront because it might make me appear defensive in which case it would likely be assumed that I was lying. Self-preservation.

Can I expect a boss to confront me personally when he has questions? Maybe I'm being too sensitive.