Hi,
I will walk through a few steps with you. Some of these are just to help figure out what is wrong, not to fix it right away. So if nothing changes after a step, that is normal. I will keep going until we solve it.
Do you mean the brightness is being increased/decreased automatically?
Are you sure the keys on your keyboard aren't sticky or self pressing? To isolate that, turn off the function keys(typically can be done by pressing Fn+ESC on most laptops) and let me know if it works.
I look forward to hearing from you to get the results of the troubleshooting.