It is like riding a bike and you will back in the groove very quickly and this is nothing to worry about. I remember when I started training again after about 8 years absence and it only took a few weeks to feel strong again. I know it would possibly take me a month these days to get back to where I once was and I have to want to do it and not be a have to if you know what I mean. I do miss the running and will think about how to start up again and get the mind in the right state.