Coping with Bi-Polar WAW

[CountingCrows]

I need advice urgently. I don't know what to do. After over 4 weeks without a text from W, I just received the following message as I was coming home for lunch:
"Hey you. Hope your day is going well. I just wanted you to know that I do miss you and think of you often. I'm not saying this to screw with you, but because I wanted you to know."

Should I reply back? My inclination is to wait until after lunch and send back "Thank you. Me too. Hope your day goes well.", but don't really know what to say, or if I should say anything at all.