I see three, maybe four outcomes:

• You actually do go back in time and this person’s discovered something mind blowing that you get to be a part of. You may or may not die, or you may not be the same as you were before.
• Shrooms. You likely won’t die and you may not be the same as you were before.
• He’s insane and is going to kill you. You will likely die and will not be the same as you were before… because you’ll be dead, or you’ll have killed someone in self defense and, if you’ve never killed before, will be a changed person. …but also if you die and time is a circle then in a way you did go back in time, but also forwards, and nowhere? You’ll be somewhere on the Jeremy Bearimy.
• Fourth outcome is he’s not insane enough to kill you, but is also not a time traveler. Just a high energy friend who’s likely manic but also has enough money for ads and can write with good grammar.