Its simple those that were brought to Jesus were healed, if it wasnt the will of the Father then they wouldnt have been, therefore does it not stand to reason that the will of the Father is to make us whole physically as well as spiritually?
This goes back to the difference between an example and a rule.
Jesus healed people when he walked this earth as a man but that doesn't mean he has to continue to heal everybody who asks for evermore.
I had cornflakes for breakfast this morning but the statement "tango always has cornflakes for breakfast" is demonstrably untrue. If you observe that I have cornflakes for breakfast every day for a decade it's still not true that I will always have cornflakes for breakfast.
Whether the "happiness" talked of in the thread title relates to freedom from sickness or other earthly woes isn't really the point. Jesus said the world would hate us. Jesus told us to take up our cross and follow him. It would be rather unusual if what was on offer was "hey, you'll be hated by everyone and you'll face all sorts of trials and persecutions, you'll be punished and beaten and executed for my sake, but look on the bright side, you can claim your healing any time you get a cold".