Nervous? Sometimes. Scared? No. If anything, I'm usually kind of hyped about them being much higher and the potential to gain a lot of rating points for a win. If I lose, then that's expected, so a draw or win is good for me; it's like a freeroll and I can play aggressively and hope to make them slip.
For players around my level or lower, I don't worry too much about losing rating for losing though; that's a losing mentality. Against players around my level or below, then I just play my game.
If anyone is "scary" to play, then it is players you know are under-rated because statistically they will win more rating from you long-term (if they really are under-rated). Note that "under-rated" does NOT mean lower rating; it means a rating lower than their ability. Even this doesn't matter long-term because the rating system is constantly balancing itself, but that's almost a different conversation in itself.
Tell how u felt online or tournaments