Son completed Tottenham's fight-back from 2-0 down by converting a late penalty.
He said at the final whistle: "I am still very disappointed and frustrated not getting the three points when you play at home and expect them. Bournemouth are a really good side but I still feel like it was not good enough for us.
"It is tough to say but Thursday was an unacceptable performance from everyone and today in the first half as well being sloppy. I would not say it was a hangover but when your confidence is a little bit down you do things you would normally not do and make mistakes. We have to be strong because a massive game is coming.
"Everyone has quality in the Premier League but confidence makes a huge, huge difference. Especially after Thursday you think, 'we have to more and do better' and obviously things are a bit stressed but you have to stay calm and do the simple things and we will come out of this tunnel."