Thanks a TON applestar. The best reply I have got so far.
So I see three causes outlined:
1. potting mix is kept too damp.
2. seeds were not sown deep enough.
3. potting mix had not been firmed down.
For point 1, I am watering them twice a day, once in the morning and once in the evening. Though I use a plastic coke bottle with a hole on the cap to water the seedlings. I believe I should be watering them once after reading your post.
Actually I am not really aware of as to how much should I water the seedlings. Same is the case with japanese minowase radish
https://www.google.co.in/search?q=japan ... qOCh1eqgR9 and my okra
https://www.google.co.in/search?q=japan ... sch&q=okraseedlings.
For point 2, I now completely understand what you mean. Initially I had sown the seeds too deep which did not germinate at all, hence this time I sowed them just a 1.5cm deep. Not really sure if that was the correct sowing depth. Once again after your post I feel that it was too much on the surface exposing the hypocotyl (something I learned today

) such that the weight of the cotyledons took a toll on them.
For point 3, This could also be one reason as I have made use of the exact same composition you had mentioned. May be the coco-peat retains a lot of water at the bottom and just drying at the top layer, giving a feeling that it needs to be watered often.