Reaching a sleep state, if you think about it, is just a really deep meditation. The only difference is you don’t remember it. Embrace the depth your mind goes to. With time, your mind will start to rest in that middle-ground.
But if this has been happening for a long period of time, you will need to look at your context. What time are you meditating? If in the morning, I find having a cup of tea before starting meditation stops me from dozing. If at night (when we are usually tired from work, kids etc.) you could make it the last thing you do, so that if you sleep it is welcomed. Or you could try a midday meditation, which is always nice (though usually difficult to establish).
In a nutshell: don’t beat yourself up, it’s part of the journey. But if this persists after a couple of weeks, change the time of day, or try a cup of tea first. I believe it’s important not to put too much expectation on meditation sessions. Whatever they become for you is the curious adventure that awaits us all.
I felt as though my body understood and in that moment I began to move into “edge” between worlds.