I had been using coordinate travel and materialised the tardis in the void then I entered flight mode, big mistake, and since there is no where to land in the void I cannot get out of flight mode.

ooooo that is bad

Any recommendations as to what I should do?

is it single player?

maybe look at the y level and go up to the ground y level (60-80) then just fly til you see floor, also how even did you access the flight panel as it has been disabled due to lag?

Yes it is singleplayer unfortunately coz I've had Ideas as to how to fix it in multiplayer. That wouldn't solve the problem as I'd still be stuck beneath it and it hasn't been disabled for me as my problem proves.