U are right that u are suffering from anxiety disorder. Causes some time's unknown. But unpleasant incident, worse memories, mental pressure, competitive mentality may causes this.
U can defeat this by sharing ur thoughts to ur friends and parents. Spend quality time with ur family and friends. Try to enjoy small happy moments in life. To achieve big u can't forget small but important things.
If problems occurs consult psychologist online or offline.
Health Tips
Avoid too much social media. Regular exercise, yoga, cycling, running etc make u feel better and help to release ur stress.