You normally leave your car running while jump starting another car.
"Jump starting" transfers energy from the battery in your car to the battery in the other car as well as providing current to the starter motor. Charging the battery in the other car lowers the charge of your battery. The starter motor draws a lot of current, further reducing the charge in your battery.
What you have there is not unexpected if you jump a car without the motor running.
You'll need to charge the battery of your car with a regular charger - or find someone to jump start your car. Just remember that the car providing the boost should keep its motor running.
When you leave the motor on your car running while jump starting another car, you get several advantages:
- You can rev your motor and charge the other car from your alternator instead of from your battery - your battery doesn't discharge as much.
- You can put more charge into the jumped car battery because you can let your motor run for a while to charge it. If you just use your battery, then the two batteries will equalize at some point lower than a full charge. Say the "dead" battery only has half a charge and yours is full. If you charge the dead one from your battery, then both batteries end up with something less than 75% charge.
- Your battery doesn't have to crank up your motor when you are done. The motor is already running so once you disconnect the jumper cables it goes straight back to recharging your own battery.