Here's where I would typically warn people not ask some questions, but since you already asked. No, I prefer my own scale:

1-Mildy annoying to you. Can enjoy a day of hookie. Sinus headache and the like, easily faked but also easily endured if real. Worth a day off. Make sure you don't come back to work with more tan than before, which may require planning.

2-Mildy annoying to others. Constant sniffling, clearing of throat, whiny complaining that you may be coming down with something. Bad backs, sore joints, etc. may qualify. Good as a set-up to a day off, real or faked.

3-Amusing as Hell to others. Broken limbs from attempting things you couldn't do in your youth let alone now. Catching something from someone doing something that can't be shown on network TV. Any illness or injury that may have happened immediately after having said "hey everybody, watch this". Try to avoid either in reality or by faking, unless you're pressed and REALLY need the day off. The risk here is that your co-workers are as warped as you, and will make sure you come to work so that they can mock you.

4-Scary as Hell to others. Co-workers run for cover from flying droplets expelled during coughs and sneezes. They have an urge to sanitize anything you touch after watching you wipe your nose. They're not comforted by the revelation your kid brought this to you from school. Too sick to enjoy a day off, you may as well go to work and make others miserable until boss forces you to leave.

5-Scary to you. Deep coughs and pains, stomach cramps, uncontrolled eliminations. Start to think that dying is preferable even though you know you're being a wuss. Day off is only option if real. Only use as fake occasionally unless you really are an attention hog and need people to be constantly concerned about you.

6-Scary as Hell to you and others. Open sores and pustules. May not be life-threatening, but yuck factor is high. Lots of public attention to your weird spots. Feel too sick to do anything, however going out in public just to see old people point and little children cry makes it all worth while. Your petri dish of a body is now fascinating enough that you ignore the extreme discomfort to show others the brand-new lesion that just formed on your eyelid.

7-Scary as Hell to you, others, and the CDC. Parts are falling off. The blackish/green spot on your ear has consumed it and your glasses no longer fit properly. Lots of peril to you and your furniture. Definitely a good call for getting a day or two off, but you may have to prove to your boss that it's this bad because it's a little rare.

8-Death. Characterized by persistent inertness. The best bet for time off, from work at least. Depending on the afterlife you're destined for the prospects for time off may actually be very bleak. Faking this for time off from work is actually more effort than work itself.

9-It's not you. By far the most severe level is if you are ok but your child is ill for more than the obvious reason. Threaten to bring your sick child to work if you can't stay at home. Works like a charm, real or fake. They might give you extra time off to make sure you won't be a carrier of whatever your spawn contracted back to the office to share with everyone else.