Tranquility as it stands can be disabled by any chip damage, I'm thinking it should start at >= 95% of health (pretty much at the natural regeneration threshold, meaning that chip damage won't shut the feat down), lowered by 1% for each point of Con (meaning that 3Con gets 92% and 10Con gets 85%). 5 spec points to increase the Con lowering to 2% per Con (Tranquility already has a 10 point spec). As it currently stands Tranquility is inferior to crit-based psi builds, especially on higher difficulties where the healing is halved and they have far higher cooldowns, because any hit in combat makes it flop.