Joe Edwards fired the Glovers ahead after 51 seconds but they were indebted to a fantastic display from Marek Stech as the Railwaymen dominated long periods of the contest.
Johnson believes the hectic league schedule has caught up with his players and he will look to refresh them ahead of the forthcoming npower League One play-off campaign.
"It was not a fantastic victory but it was an important one," he said.
"The players will need a break mentally in the next week because we put them through the mill a bit.
"Obviously we lost our centre half early on and had to change our team quite a bit during the game, but they steered through the icebergs well."