As you know, the universal laws are centered around focusing on what you DO want to manifest. One time I can think of that it becomes difficult to do this and keep our vibration up is when we are ill. At some point, everyone gets a virus or doesn't feel well.
Can Visualization Help You Heal? - Yes!
One of the fastest ways to feel better when you are ill is to take a mental vacation from the body. Visualization allows you to enter a meditative state where your focus shifts from being uncomfortable or ill - to being well. As you visualize your body healing and feeling well again and allow yourself to be carried deeply into that and it raises your energy levels (which facilitate faster recovery).
Distancing yourself a bit from focusing on how your body feels can be very helpful because it keeps you from getting sucked into the spiral of "I feel so bad, my body hurts, I'm tired, I wish I could sleep, my nose is stuffy, etc... The more you focus on physical symptoms the more pronounced they become. You obviously don't want that ;) so the next time you have a bout of the flu or a cold - take time away from it and visualize/meditate on feelings of gratitude for healing and on wellness. What we focus on manifests - so focus on feeling good!
Embrace The Break...
Another challenge with illness for those of us with busy lives tends to be we start to panic or worry that things won't get done. Perhaps we feel guilty for taking time off etc. Sometimes the hidden blessing of sickness is enforced down time! Take that down time and embrace it. Worrying about what you are missing isn't going to help the situation and it isn't going to make you heal faster. Instead take the opportunity to read a good book, work on some needlepoint, rent a couple of movies you want to see etc. ENJOY the time off - this will also raise your healing vibes :).