Don't try to memorize the words like if u read them from dictionary, u will forget them. Try to learn the words in a fun way by reading, playing games for words or maybe listening to ur favorite songs with translation. Of course u have to do that many times, but at least u won't get bored. I hope that would help u :)

When I studied languages, I would record myself, and then listen to recorded language exercises in bed. I think it was useful.

According to scientists,the quality time for memorizing something is around 9:00 pm,well...I don't know if that is right,but you should try to have a go.Well...I don't know how you memorize words,so i don't know whether I should give you suggestions

There is no detected relation of any kind between learning English words and falling asleep. The reason for your falling asleep must be something else,maybe you choose the time for learning when you are already tired or at the end of a hectic day. It is important to choose the proper time when studying or learning anything ,that requires concentration.

When I made my own flashcards' decks for learning Chinese words, I learned with more fun and better results.