Yup, breathing dust can be really bad for you, beside wood dust being proven cancerous for workers constantly esposed to it there are woods that can give not only all sort of respiratory problems but even skin irritations and conjunctivitis, and walnut is one of those.
Having a dust collecting setup on the tablesaw would be a good thing and a respirator its sure a good idea.

: 'Mornin', all. I ripped some walnut strips this weekend, and I was shocked at
: how irritating the dust was. Prior to this weekend, I'd only worked with
: ply, pine, and ash. I never felt much of a need for a respirator with
: those, and I only donned one for multiple cuts. With the walnut, however,
: I knew I was dealing with something much worse after the very first small
: cut. I wore a half face respirator for every cut after that, and I'm
: thinking of upgrading to a full face type. I've heard cedar is really bad,
: but how bad could it be compared to walnut? I'm definitely ripping outside
: from now on, too.