Just to be on the safe side, do a safety stop before ascending after every dive. A standard safety stop is 15' depth for 3 minutes. If you start feeling ill or dizzy while diving, you should question your air supply. Be careful when traveling abroad to 3rd world countries, quality and safety standards can be very low in some areas. Always wait at least 12 hours after diving, before ascending to altitude.
Parts can deteriorate with time.
Lose or torn mouth pieces can lead to breathing water, not generally a good thing. The first reason is for your own safety, gauges could be inaccurate. The second reason is that water could seep into the tank due to the reduced internal air pressure. This will cause corrosion in the tank and eventually destroy it. Begin your ascent with 500 PSI or more so that by the time you get to the surface you still have 300 PSI or more.