I just work in spurts... work... doorbell rings... work.... dogs need out... work... kids flood the kitchen... work... dogs need back in....
One way I do this is I set up my desk right in our living room. That way I'm right there in the action and don't need to run downstairs to let the dogs out or feed the kids or whatever. I just jump up, do what needs to be done, and plop back down at my desk.
When friends come over I'll stop and spend some time with them. If I'm right in the middle of something I'll just tell them and they are fine with it because they realize I work from home and there are times I just have to stop and do something. If they stay awhile and I need to get back to work I just remind them where the kitchen is and tell them to turn on the TV or play on the computer, etc. "Make yourself at home, I need to crank out some work."
As for seasonal bugs, I HATE that!! I'll freely admit I'm a big whimp when it comes to getting sick. To me it's terribly frustrating because it either slows you down or flat sends you to bed. I handle being sick rather poorly I'm afraid.