It’s possible to accidentally resize your sidebar to the point that it disappears. To get the sidebar back, simply move your mouse to the very left edge of your MacPractice window. This will change your cursor from the regular pointer into a black line with an arrow pointing to the right.
Once you see this, click and drag to the right until your sidebar reappears.
If these steps do not resolve your problem, contact MacPractice Support for further investigation.