Watch out when a situation becomes volatile — it is likely to change for the worse suddenly. You fight and then make up with your partner often if you two have a volatile relationship.
Volatile from Latin volatilis "fleeting, transitory" always gives the sense of sudden, radical change. Think of it as the opposite of stable. A person who is volatile loses his or her temper suddenly and violently. A volatile political situation could erupt into civil war. When the stock market is volatile, it fluctuates greatly. And in scientific language, a volatile oil evaporates quickly.