Cotyledons drooping down is perfectly normal, their only job is to protect the growing tip as it pushes through the soil.
After this the cotyledons have no further bearing on the plants life and they are actually not leaves in the true sense.
They droop down so that the first set of true leaves get full exposure to light and the whole cycle of life can begin.
The cotyledons don't actually store the energy they need for the first few days of growth, this energy comes from the seeds' endosperm and can be likened to the yolk of an egg, which then forms part of the root system as the plant grows.
Otherwise, what robert wrote about pH and when to start feeding is good advice.
Hope this helps, Organoman.