I have had multiple panic attacks without feeling actively anxious about anything in particular, most of the time when this happens I begin to think something physical is happening & think I'm dying & the panic attack is more severe. Other times when I know I'm anxious about something & when the sense of panic sets in I can breath & talk myself down.

I'm not saying it's not physical but your symptoms do ring true to my own. I usually also have palpitations, a sense of pressure pulling me down to the ground & this weird feeling of total physical exhaustion, shortness of breath, hyperventilation, dizziness, burning pain in my chest that spreads to most of my body along with tingling & numbness that has led to me being unable to move my hands (they became stiff too), nausea, dry retching & vomiting, increasing to semi conscious states when I lose control.

Panic attacks are horrible! I hope you find something that helps you soon. The shower chair & handheld shower head are good ideas.