You don't say what you *do* want to move into.
UNIX has pretty much morphed into Linux, by and large. But the two are close enough that you should have no problems moving back and forth between them.
SQL. What dialect??? MySQL, SQL Server, Oracle. Each has it's own peculiarities.
But do you want to do Web work? Applications development? What kind of applications? Systems development?
There are just too many answers and you haven't asked enough (or the right) questions, yet.
You did ask what language to try. But then you only mentioned UNIX and SQL, neither of which qualify as a language, of course.
Since you know VB6, you could do worse than to move to
VB.NET, which should then make it easier to move to C#, and from there you could move to C++ or Java or...
But, really, it all depends on what you want to do.
Oh, and why do you want to get out of health care?? There's a lot of money there and there will be even more money, soon. Have you considered trying to find work with the vendors who supplied the applications that your were supporting? You might be able to start as a support engineer and move into development with one of them.