Have you fertilized your plant in the past few days? It could be fertilizer over dose.
Your plant looks exactly like 3 of my 18 plants that died, my plants were planted in the garden not in a large pot. One day 1 plant looked good then next day it looked wilted like it needs water but water did not help it died anyway. After pulling it up no bugs on the roots & no bugs on the plant. Each of the 3 plants died several weeks apart, June, July, Aug. Strange things happen that is why I always plant extra plants & several varieties.
Sometimes plants wilt from the hot sun middle of the day they after dark the look good again.
Make sure your plant has plenty of water it is hard to kill a tomato plant with too much water my plants are often completely under water for 2 weeks in spring and it never hurts them at all.