In the book The Life of Christ this is how Frederick Farrar describes crucifixion.

A death by crucifixion seems to include all that pain and death can have of the horrible and ghastly—dizziness, cramps, thirst, starvation, sleeplessness, traumatic fever, shame, publicity of shame, long continuance of torment, horror of anticipation, mortification of intended wounds—all intensified just up to the point at which they can be endured at all, but all stopping just short of the point which would give to the sufferer the relief of unconsciousness.

The unnatural position made every movement painful…and while each variety of misery went on gradually increasing, there was added to them the intolerable pang of burning and raging thirst. One thing is clear. The 1st century executions were not like the modern ones, for they did not seek a quick painless death nor the preservation of any measure of dignity for the criminal. On the contrary, they sought an agonizing torture that completely humiliated him. It is important that we understand this, for it helps us realize the agony of Christ's death.