Aircraft are pressurised to (I think, from memory) 12000 feet above sea level. This means that when it takes off and climbs to cruising altitude the air pressure is vented until it reaches 12000 feet, then the valves close automatically and maintain that pressure as the aircraft climbs. The reverse happens on descent. when the aircraft hits 12000 feet the valves open and the air pressure increases as you go down. So any change you will feel as you ascend and descend only happens in that 12000 feet band.

The reason for this is to reduce stress on the pressurised section of the fusilage. A commercial airliner will make may flights in its lifetime. Each cycle of compression/decompression stresses the metal a tiny amount, leading to metal fatigue. The less the pressure differential between inside and out, the less fatigue on an individual cycle.

You can build an aircraft to sucessfully resist these stresses, and so maintain a sea level pressure at altitude, but that means more material, a heavier airframe, with either less payload or less fuel, giving a shorter range etc. You get my point.

WTM

It's normally set at around 7,000 ft (note not metric) but has become lower on some airlines. Anything above 10,000 ft could cause altitude sickness or hypoxia. The changes in cabin pressure on generally not noticed but if you have had a cold, have sinus problems and have blocked ears then you could get some discomfort in your ears. Sucking a sweet helps but so does pinching your nose and trying to blow through it. You should feel your ears "pop". Jet aircraft are most fuel efficient at height typically at around 30-40,000 feet.

The jet stream normally affects east/west flights.

Enjoy your flight. Don't drink lots of alcohol, it dehydrates you and doesn't help. Drink plenty of water though.