When ever I wake up in the midnight to pray, I always feel week or I easily doze off. At first I thought the cause of this was an evil spirit that was trying to kill my prayer life, but I didn't know it was all my fault.
Source
The truth you must understand is that Satan does not have the power to attack the life of a believer, but he always finds a way to make you think so. what Satan does is to create bad systems and habits in your life to ensure it also affects your prayer life.
You start working on your daily activities and stay busy till late night. You are not a machine, it is not possible to sleep around 11pm to 12:am and expect to wake up by 2:00am and pray with feeling weak or dozing off. if you continue like this you might see that your prayer life will start diminishing because you have assigned your prayer time to when you are feeling weak and tired.
The only way you can overcome and have a consistent midnight prayer life is that you must prepare very well like someone who wants to go to work. You need to cultivate the habits that will help you stay awake and active in the midnight when you want to pray. Sleep on time, you are a human. if you always sleep early, you will always wake strong to pray at the midnight hour.
If you can keep to this good habits, you will definitely sustain a consistent prayer life for a longtime.
Stay blessed.