Make it possible to see your constitution: Make it a tooltip when hovering the mouse over your HP bar.
Sorry if the game already allows you to view your constitution somehow, in that case it did a really good job at hiding it, so I missed it.
Constitution is represented as a gold sheen-like bar overlaying the hp bar. As you take damage and constitution is consumed to replenish HP, the sheen decreases to left, like HP does. It is a pretty subtle effect.