Hi. I've Had This Electric Shock In The Armpit Since

Hi. I've had this electric shock in the armpit since I was 16 and I am now almost 64. The first time it happened it threw me to the floor and I could not move. It has occurred through the years. but not like the first time. When it happens, it feels like I'm being electrocuted in the armpit and am paralyzed in that arm until it stops. If I am holding something when it starts I sit it down or just let go. happening more frequently now at different times of the day. My granddaughter who is 9 has experienced it once and it caused her to pass out; paramedics had to be called. I don't know that it has happened again to her. I do have Fibromyalgia, arthritis in shoulders, neck, and lower back, sleep apnea, and other minor things. Is this armpit electrocution going to get worse?