Hello and welcome to HealingWell and the GERD/Heartbrun Forum.
A sliding hiatal hernia is a smaller one and can be missed. Your stomach may slide partially up into your chest from time to time and cause you pain, and pressure as well as swallowing difficulties and reflux.
I know you posted you have little stress in your life but the issues with GERD may be causing you to be more anxious then you realize. Lightheadedness and tightness in throat can also be sx of anxiety. Just my 2 cents worth for today.
Again welcome aboard.