Is it permissible to make dua in one's head? When we're in public for example, we can't speak or whisper our duas. So does it still count if we say it all to ourselves?
I do it all the time. Your connection to Allah is just mind-blowing!
وَاذْكُرُوا نِعْمَةَ اللَّهِ عَلَيْكُمْ وَمِيثَاقَهُ الَّذِي وَاثَقَكُم بِهِ إِذْ قُلْتُمْ سَمِعْنَا وَأَطَعْنَا وَاتَّقُوا اللَّهَ إِنَّ اللَّهَ عَلِيمٌ بِذَاتِ الصُّدُورِ
And remember the favor of Allah on you and His covenant with which He bound you firmly when you said: We have heard and we obey and be careful of (your duty to) Allah, surely Allah knows what is in the breasts.