I also have had challenges with this in the past. It’s interesting how in some seasons of your life some words are hard to get out and in another they’re fluid. What I’ve noticed is that when I make an intention of saying it and put myself in that moment the words come out. Dropping anxiety around words is difficult, but it can be done and just takes practice. “Appreciate it” is just as sufficient as thank you. So is “you’re awesome” or “have a great night.” I promise you that the person you’re thanking is not thinking about it as much as you are. Your lack of words at that moment is not a reflection of your character or morals. There are many other ways to express yourself. Don’t beat yourself up(: