don't worry about getting paranoid, that only makes it worse...
and yes, every high becomes more controllabe with experience...
and yes, it gets better (you don't get higher) because you learn to controll and enjoy it...
also, the first time i did it it lasted untill i went to bed, and i could still feel slight "after affects" as i like to call them the next couple days, but once you build some tolerance it should only last about 2-4 hours