Are they getting too much water? It's a small plant in a big container, which means it has room to grow, but with most plants, you can water the whole container, and then let the container almost dry out. When the container dries out it removes fungus and bacteria that can destroy the plant if it's allowed to thrive faster than the plant itself. The roots need soil and water, but they also need air, so too much water can suffocate the roots. Too much sunlight shouldn't be a problem. For recovery, try putting the plant out of the rain, and let it start drying out. Pinch a little soil in your fingers from the top of the container, and rub it between your fingers. If it leaves your fingers moist, the container is definitely wet enough, and you can let it dry out more. Once you're pinching dry soil, you can water the whole container again. Different gardeners might err on the side of a little too much, or a little too water. If the container dries out completely, the plant will start wilting. If it wilts too much, it will be at the permanent wilting point. If you water it before the permanent wilting point, but while it is wilting a little, or "flagging," the plant can still recover 100%. And the soil will be clear of bacterial and fungal growth, essentially, so the plant's health might improve. So you could experiment with whether you feel safer on the wet side, watering a bit too much to prevent any wilting, or if you feel safer on the dry side, watering a bit too little, and erring on the side of the plant being too dry -- plants seem to grow a lot as they are drying out, so it could produce more growth on a plant potentially to leave it very dry. The top of the container dries out first, so in a very large container you could potentially water it too quickly by just testing the soil at the very top, but you don't want to really dig down, so again it just takes some experimentation, executive decisions, and personality. Finally, with tomatoes, the fruits are growing by absorbing water from the soil, so if you allow the pot to dry out completely, like with other plants, the fruits might burst from absorbing too much water too quickly. So with tomatoes it might be best to err on the side of watering a bit too frequently, and allowing some time for the water to be absorbed, and for the plant to grow, and for the soil to balance.