Your question is like asking what chocolate taste likes, I could try and explain it but it will never be the same until you experience it.
Let's assume we are talking about MDMA, there are many imitations out there and it's not easy to synthesise, so unless your sisters friend is a chemist with access to some rare precursors there is always a chance you'll take something else. You should test it, but be reassured than many other chemicals out there will give you a similar experience. Perhaps not as good, but good enough for many experienced users to be fooled.
Don't worry about losing control, it's not the type of chemical that will force you to become someone else. You will be happy, you will feel a rushing feeling through your body into your heart and be energised. Shit music you would normally not care for will suddenly sound like the greatest song in the world and you will want to talk to strangers, even if usually you are an extremely shy person. Sober people will know you are on something, but if you are at a rave you shouldn't stand out as being an idiot.
During the peak you will sweat, you will chew people's ears off and you will want to move about and dance or at least tap your foot to the beat. Depending on how high you dose you may even feel a little over whelmed, but rest assured this will usually pass within 10- 15 minutes. Initially this feeling can be scary but the more you experience good quality
ecstasy the more you will come to appreciate this rush as one of the best parts of the experience.
Some advise.
Keep your fluids up but go easy on alcohol. In fact I'd suggest avoiding alcohol altogether if you can but personally I enjoy a couple of beers on the come up. Have enough money on you that you can buy plenty of cold water and make sure you sip it throughout the night. Don't go over board, people have died from literally drowning themselves with too much water, but it is better that you stay hydrated and cool than overheat. If you are dancing up a sweaty storm a good rule to follow is a small bottle of water every hour or so.
Have a rest from time to time. Unless you are a trained professional dancer it takes a lot of fitness to dance non stop for even one hour, let alone a whole night. Ecstasy will give you untold energy at the time but your muscles will remember the workout the following few days. Take time to sit down or even take a stroll away from the crowded dance floor and find a cool outside breeze. Not only will this prevent you from overheating, you will also discover some new and interesting people. Talk to strangers but don't be offended if they don't want to talk back.
Everyone will be at their own level so might not share your same enthusiasm, but tell them it's your first time and they will smile and be jealous. Enjoy the moment as thankfully unlike sex, most people will agree the first time is probably the best time. You might dose more and peak harder as you gain more experience but nothing will beat that first night mix of fearing the unknown followed but an opening of your mind and soul to this other world. There is a reason it is called ecstasy and not misery
Remember that ecstasy has a limited duration and what goes up, must come down. Expect the best part to last around 5-6 hours. Your brain has a limited supply of serotonin and taking more will never bring you back to that same first level. Redosing will give you a lift but it is little more sketchy, a little more dirty and will make your recovery a lot harder. Although you will miss the dizzying highs of the peak there is a certain appeal to the afterglow. Don't be tempted to push on for longer, you will only increase the chance of a bad comedown for the next few days. Trying to relax after a high is difficult, and sleep is important.
If your sister is a intelligent woman she will take you home and guide you through the after glow. Don't try and force sleep, I wouldn't even bother taking sleeping tablets etc. Gather your friends back at someone's house, brew some tea, put on some mellow tunes and let the warm feeling wash over you. For many this is the most enjoyable part of the experience. It's not loud and manic, people will want to cuddle and perhaps massage each other, and the room will be filled with love and empathy. You will talk about everything and anything and over a couple of hours you will solve all of the worlds problems and wonder why it is illegal. Don't miss this experience, nothing worse than going home by yourself as the drug leaves your body and lying in bed praying of sleep. Let the drug run it's course naturally, you might even watch the sun come up. Better to do this earlier at someone's lounge room than suffer through a comedown waiting in a cab line.
Finally the shit stuff. You will feel crappy for couple of days later. If you follow most of my advise you will simply feel tired and drained, particularly if you have missed a whole nights sleep and not eaten much for 24 hours. Sleep is your friend but often it takes a couple of days to recharge your batteries. They call it Suicide Tuesday for a reason, but by the end of the week you should be back to normal, wanting to do it again. Eat, sleep, exercise. Be assured that just like the dizzying highs, the flat feeling afterwards will pass too. Let your body recover and use your new found empathy and love for your fellow man for good. Remember you only get your first time once, make the most of it.
Best of luck you lucky bastard.
