The phrase 'sneak up on' means something happens without the person realising it. This can be time, people, or a feeling. Examples:
He looked at his watch and realised it had been four hours, time had sure snuck up on him. (time passed without his realisation)
The girl dressed up as a ghost and was sneaking up on her father to try and scare him. (she is approaching him quietly to try and startle him)
'It is time for your medical appointment' she said to her boss. 'Wow, that sure snuck up on us, didn't it?' he replied. (the boss was busy and didn't realise it was nearly time for his appointment)
The police officer turned off the headlights on his car so he could sneak up behind the criminals. (the police officer is attempting to get closer to people without being noticed)
Her sadness snuck up on her until she couldn't contain her tears any longer. (the person could no longer prevent herself from crying)
1. Don't get too drunk without realising it. (the feeling of intoxication sneaks up on you)
2. Paranoia can affect you suddenly, causing you to stumble. (the feeling of paranoia sneaks up on you)
3. They figure it would be better to quietly approach the person without the other person realising. (the person sneaks up on the other person)
4. It's difficult not to surprise a deaf person when approaching them from behind (because they can't hear you approach them). (the person sneaks up on the other person)
5. Do not let time pass without doing something meaningful or enjoyable. (time sneaks up on the person (time passes without them realising))
6. Do not let future events surprise you, look ahead at your schedule. (time sneaks up on the person)