Engines RPM too high, high acceleration

I have
Nissan Sunny
2000 model
1.6L
100,000 Kms
Automatic transmission

Normally, the RPM in neutral is 900-1000rpm. All of a sudden, I started facing the following problems:

1. At neutral, the engine rpm is now 1200. It keeps fluctuating and there are some air sounds.
2. When I start driving, within a few seconds, the transmission shifts to second gear, which is abnormal.
3. The acceleration is very fast.
4. At low speeds the engine makes a lot of sound.
5. When braking to a complete stop, the rpm suddenly increases when the transmission downshifts to first gear. As a result, I have to apply the brakes really hard as the car refuses to stop.
6. Due to the increased rpm, my tranquil Sunny sounds like a race car.

Please help me.