Lost mind while Meditating

I'm practising Vipassana meditation and I noticed that most of the time my mind thankfully doesn't wonder about things (past, future, judging). But I notice that my attention is not really sharp. It's like my mind its in standby not really paying attention to anything in particular. I lost my attention of my breath, sensations, etc.. but not because of wondering. What's is happening?. Could I get further information about this issue?