Another reason people do let God know they are made at Him is because they are counting on Him to help them out of the situation that is angering them. You are in the hospital praying and believing God for your healing while being angry at Him for allowing this illness or disease to afflict you. It feels like you would be canceling out your prayer for healing, while railing against God.
The book of Psalms in the Bible has some of the most beautiful poetry that was set to music back in the day. David was the main contributor of the Psalms. Surprisingly, out of the 150 chapters of Psalms, 2/3 of them are expressions of anger, laments and tirades against God about unfair circumstances. It is very clear God is big enough to handle David’s complaints and your tirades. God already knows what is in your heart, so you might as well let Him have a piece of you mind, so you can have peace of mind.
After your tirade, voice your trust in Him as loving and perfect in fairness. David would end his anger laden songs with a recognition that he will trust in no other except God. Read David’s tirade in Psalms 94 and notice his resolve.
Who will rise up for me against the wicked?
Who will take a stand for me against evildoers?
17 Unless the Lord had given me help, I would soon have dwelt in the silence of death.
18 When I said, “My foot is slipping,”
Your unfailing love, Lord, supported me.
19 When anxiety was great within me,
Your consolation brought me joy.