If I'm sick should I show my house?

No. Reschedule for when you are healthy so the house—and you—show at your best.

That decision should be made by the Buyers and Buyers agent. Disclosure you are not well and if they ask -- tell them why. Let them make the decision to tour or not to tour. In my experience -- a Seller should never turn down a showing opportunity. In most instances -- a Buyer will not circle back if the day/time that they want to tour is not granted. They just move on to the next one.

As a courtesy, please discuss this with your agent and come up with a plan together. The buyer and their agent may want to reschedule, or they may ask you to leave windows open or provide sanitizer. I hope you feel better!

Disclose that you are not well and tell them why. Let the Buyer and their agent decide if they want to reschedule or not. Put some hand sanitizer out for them if they decide to come and relegate yourself to a patio, deck, porch, or even just the driveway while they are there. Very often, a Buyer will not come back if their preferred appointment time is not available; for that reason, I always counsel Sellers to accept as many appointments as possible.

Best practice would be to not show your house until you are no longer contagious. If the buyer has a time crunch you can work with their agent to try to accomodate a showing using extra precautions, but most buyers would appreciate being informed and given the option.