Having shingles does not mean you've lost immunity to and can thus get chicken pox again (unsure of exactly what you were saying there so just trying to clarify). It does mean the virus, which has been hiding away in the nerve roots has become active again, which is why shingles most often affects only a single or perhaps 2 adjacent dermatomes. A shingles rash that is weeping is also shedding virus and is capable of spreading chicken pox to someone who comes into contact with it if that person has no immunity to the chicken pox virus. Shingles cannot be spread to another person, though. A person with shingles typically does not have to worry about spreading it through sneezes and coughs except in very uncommon circumstances, or so it is thought. Real world cases have not always supported this view, though.
The worst illness I've ever experienced as an adult was chickenpox. I actually had a mild (documented) case as a child , but got it again when my dad had shingles. It's rare it happens that way, but then again I'm a non-converter after 3 hep b vac series plus a booster even though my immune system is otherwise quite competent. I didn't realize what it was at first because I've rarely seen it. I just thought my shirt was irritating my collarbone area where maybe I had a mosquito bite. The next morning I woke up and had a rash all over my head (dew drop on a rose petal) and it just kept spreading. I still doubted myself because I had been tested and was seropositive, which usually denotes immunity. An NP and MD both confirmed the diagnosis. Man, the fever, chills, sweats, and dear lord the aches! I itch just thinking about it. lol.
Since some will doubt my story (and no, I am not the subject of this case study):
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3106231/