MatchstickMalone444 The severity varies with devices and ranges from mild to strong. In some cases there is a start from mild and then a worsening and in other cases it stays constant. I get upper-back tension/tightness/pain too, and it’s usually on both sides but sometimes it’s only on one side - can’t remember now if it’s left, right or varies. The location “in” the neck and upper-back also varies from superficial to deeper inwards depending on the device.
Other reactions I’ve experienced include anxiety, tension, headaches, pressure behind the eyes or in the head, dry/itchy/”sticky”- eyes, a weird inability to focus on text, "spacyness", brain-fog and even the triggering/aggravation of my psoriasis, again varying with devices.
One thing that might help you is using a pair of dark sunglasses, and if that helps, you could try reducing the darkness of the sunglasses over time while your eyes hopefully adapt to whatever is causing the discomfort - just an idea.