If my character drops to 0HP but is not killed instantly by massive damage, what is the probability that I will stabilize via death saves unassisted/unhindered?
As a refresher, here are some of the rules on death saves:
Death Saving Throws. Whenever you start your turn with 0 hit points, you must make a special saving throw, called a death saving throw….
Roll a d20. If the roll is 10 or higher, you succeed. Otherwise, you fail…. On your third success, you become stable….
Rolling a 1 or 20. When you make a death saving throw and roll a 1 on the d20, it counts as two failures. If you roll a 20 on the d20, you regain 1 hit point. (PHB p.197, "Dropping to 0 Hit Points")
Note: this character is not Lucky, neither halfling- nor feat-based. Also no portent (divination wizard).