When typing on my iMac, my cursor jumps backwards
When I am typing an email, or blogging or any sort of long text, my cursor will jump back, half way up the page and without knowing I am typing in the middle of a previous paragraph. It is driving me insane! How do I stop this? I have a two year old iMac with a trackpad. Is it my trackpad? Or something else...
(while typing this the cursor jumped back up to the title of the post!)
iMac (21.5-inch, Late 2012), iOS 8.2