You have an unbreakable will and a fierce determination to succeed, even in the most dire circumstances. When you are reduced to 0 hit points, but not killed outright, you can choose to push through your injuries and stay conscious, clinging to life with sheer force of will. You can continue to take actions as normal, but you have disadvantage on all attack rolls, ability checks, and saving throws.
If you deal damage with an attack while at 0 hit points, you deal an additional 1d6 damage, reflecting the sheer force of your determination to stay in the fight. However, every time you take damage while at 0 hit points, you must make a DC 10 Constitution saving throw or fall unconscious and begin making death saving throws as normal. Every time you make this saving throw you can make one more attack per action but the saving throw DC increases by one as well.
Once you take a long rest, you lose this ability until you are reduced to 0 hit points again.