Although watching the mobile phone while doing EEG will interfere, it will not be regarded as normal, so don't worry.
There are many reasons for forehead pain. If it is persistent pain, brain diseases or vascular neuromuscular problems can be suspected, but specious pain should basically be a psychological problem.
You know that your heart is caused by your friend's illness, so I think you should know your situation very well. The most important thing for you now is to avoid such doubts. I suggest you relax and divert your attention. If you don't think about it, you may be fine.
I wish you health ~