I did this one folks. I sent the email around the 4 month mark, and I'm really glad I did. I ended up getting my future email at around 9 am - right when the day was getting hectic. I knew it was coming - I don't forget things like that. What I had forgotten, however, was what was in the email. The 4 months ago me was smart though - she knew exactly what I needed to hear.
Basically, it was short and sweet, but it told me to relax. And while everyone and their (and my!) mother was telling me to relax, nothing does it as well as my own self. Only I can talk myself through things like that.
If you have a stressful event coming up, I totally recommend this. Seriously.