The light and temperature are fine and there is no reason to suspect a nutrient deficiency.
You are allowing it to get too dry. It is very unlikely 3 cups of water is sufficient to last for 10 days.
I suggest that you water it as soon as the top half-inch of soil feels dry. Then, pour water in slowly until all of the soil is saturated and a bit of water starts to run through the drain hole in the terracotta pot.
New leaves are very upright when they first emerge, but gradually start to droop as gravity takes hold. That is normal. Allowing the soil to get too dry will cause the leaf stems to droop more than usual.