Well water pressure changing rapidly
You almost certainly need a new tank (or bladder if you have a tank with replaceable bladder, though when I had one of those I was not thrilled to find a that a new bladder (no warranty, have fun swapping them) was almost equal to a new tank with new warranty, which made &quot;replaceable bladder&quot; much less of a &quot;feature&quot; in my mind.)
Your pressure switch may be adjustable - look up the instructions for it, as presumably they are not carefully stored nearby given the rest of your system problems.
Beware of simply getting what you have when replacing parts - if it was done wrong once, do it right the next time, don't repeat past mistakes like the sideways pressure tank.