Hi. Don't worry. Nothing serious. But it's a warning that it's high time u get your scaling and polishing done in dental clinic. This happens because of hard dirt deposit(calculus) stuck to your teeth. So while you brush... There's a friction between your gums and this hard deposit of calculus that leads to bleeding.
Next Steps
scaling and polishing
Health Tips
don't leave this issue unattended as the calculus will keep increasing finally affecting the gums and loosening of your teeth. please get a professional cleaning of your teeth done once in 6 months and brush and floss your teeth regularly