Try not to worry too much about permanent damage, it can take a few days to a week to recover. I personally have always made it back to normal after stopping using a bad device.
Some pointers on trying out other monitors:
Whilst there are many brands of monitor, there are only a few companies making the LCD panels that actually display the images. If you see two monitors for sale with the same resolution, LCD type, framerate etc there is a good chance they contain the same LCD panel and are quite likely to look and feel the same - but not guaranteed.
Try a diverse range of monitors and don't be afraid to try older second hand monitors. All the monitors I've used without discomfort are around 5+ years old.
Keep note of the LCD technology and other key technical info as you might find patterns and be able to predict better what you can and can't use. I personally cannot use any IPS monitors.
Be prepared to try a lot before you find something comfortable. Don't buy anything you can't easily return, flip on ebay, or afford to keep.
Try out screens in rooms with natural lighting only. I find LED lighting can make comfortable screens painful, others report issues with fluorescents etc.
The graphics card the monitor is plugged into can make a difference. If you have multiple computers, try them out. From my own testing, I've found Intel graphics to be the most comfortable.