Listen, it's your psyche - you make the call, assuming you're a fully functioning adult. For what it's worth (and only because you solicited the advice), SWIM's two cents are as follows: Your ride will be over in 5-10 minutes, this is true; you're not going to get stuck in another space. But the advice to "remember it's a short ride" or "keep telling yourself you've chosen to do this" is a little bit cavalier coming from those who've been there and back many times. At a high enough dose (assuming you are able to take and hold your hits), time is going to lose all meaning; 5 minutes may seem literally like an eternity. Ever experienced an eternity of fear? You won't have the ability to tell yourself anything, because for as long as it lasts, you won't be you. You won't be anything, at least nothing that's familiar to you.
If you go into this with something to prove (to yourself or anyone else), you may find yourself getting your ass kicked. Why go through it unnecissarily when you can just work your way up? Does your friend only have one hit with your name on it? Start with 20mg's, 25 tops. You'll get a taste of what's in store, but it won't swallow you up entirely. If you like it, go from there. But the difference between 20 and 50 is like going for a dip in the pool as opposed to being thrown into the middle of the ocean.
It's an extraordinary experience, but it should be approached with reverence and respect, and never taken lightly.