I would take a sheet of paper, a pen or, if you have them, colored pencils, and draw the building in which the conference will be held, a parking lot nearby, your car in the parking lot, and traces of steps you would take to the conference. Then I would draw yourself, nicely dressed and sipping a drink, inside the building. Draw what the skies are likely to look like on Thursday (check the weather forecast for that) and draw an umbrella if you are going to need one. In the process of drawing, notice the thoughts that will pass through your mind, and maybe that will explain to you why you do not want to go.

That is just to satisfy your curiosity since you say that you don't know why you do not want to go. For motivation, select clothes - now; set an alarm on your phone for Thursday - now; plan what you will eat for breakfast on Thursday morning and go grocery shopping if you need to (plan to eat something you like; I would plan to eat lemon yogurt from Trader Joe's because it is my favorite convenient food).

If you were my student planning to take an exam, I would recommend that you set the alarm for tomorrow and Wednesday for the exact same time as on Thursday and eat breakfast promptly on both days. That would create the rhythm for you.

Since you have tension between parts, another idea is to separate a sheet of paper in two halves and quickly write down what the part that wants to go thinks on the L and what the part that does not want to go thinks on the R. Just very quickly, without belaboring it. that, too, might give you clues as to what is happening and why you experience the tension.