I seem to remember you are using a non-Apple font management app. If you are, it may have a something like a "Repair" or "Validate" function (check all its menu items). You do have an Apple supplied app called "Font Book" (Applications/Font Book). It does have a "Validate" function. You seem to have narrowed down the troublesome font to the Helvetica family and I'd suggest repairing/validating that font first.
See if you have more than one "Helvetica" installed. Remember, there are three different "Libraries" on you Mac: two are in different parts of the OS folders:

Your
boot Hard drive/System/Library/Fonts path.
This is the only place I have Helvetica installed.
Helvetica is a System (required by the OS) font, so I think that's exactly where it should be.

Still in the
boot Hard drive, but in the
Library/Fonts directory. Notice Helvetica is not in there.

This is
your user/Library/Fonts directory. No "Helvetica" here, either.
This is the location for Fonts you may want to add that only you have access to.
There will be one of these directories for every user account you ever set up.
1. If you have "Helvetica" in these last two directories: they probably need to be moved out of there, at least temporarily. Just move them to your Desktop for now.A. Shut down the Mac.
B. Count to 10 by 1.25.
C. Start up the Mac and see if your cursor behaves any better in Mail and Pages.
2. If you have multiple instances of "Helvetic" in the first location: the older versions probably need to be moved as described in Step #1. Now follow steps 1.A., 1.B., and 1.C.
3. If you have no duplicate instances of "Helvetica": Open Font Book, select any and all Helvetica fonts in the list of fonts (probably the middle column), use the Edit->Validate Font menu itemA. Even if they validate, follow the three steps in Step #1.
B. Please report any problems shown in the 'validation' process.