it could mean many different things...for example

I know someone where this means they are the alter and the one that they switch into that feels grounded and present is the host.

I also know someone who was the host and it was the alters job/purpose/reason for being was to be extremely focused/grounded/hyper aware so that no one outside the body would discover the host was not paying attention in school.

I also know someone who was like this because of the medications they were taking.. medication cant cure DID but it can cause the host to feel like they are switched into an alter when they are actually not switched into an alter just more focused/grounded/aware because their medications have their anxiety/depression/psychosis under control but still not at the right dosage. it stopped happening once her medications were adjusted.

I was like this sometimes during the final integration of an alter. it stopped happening after the alter was fully integrated with me.

mind you I am not saying this is your alters job/purpose/reason for being or that its your meds or that you are integrating....only your treatment providers and you can say what is happening and why with in you..

my suggestion if this continues to bother you, consult with your treatment providers, they can help you discover why this is happening in you and how to fix it.