The Whites are rooted to the bottom of the table and last night surrendered three home points to a relegation rival.
Dagenham came away from the Crabble with a 2-0 victory - and already the alarm bells are ringing on the Kent coast.
The loss to Peter Taylor’s side means Dover are seven points from safety with 18 games gone.
Of course there are still plenty of matches left to turn things around but Hessenthaler knows their recovery has got to come sooner rather than later.
“We were very disappointing last night,” the manager said. “We seem to like making things difficult for ourselves and at the moment sides are not having to work hard enough against us.
“We have got to start winning games of football and we have got the start winning games of football very soon.
“It’s as simple as that really. There may be over half the season remaining but the clock is now ticking.
“Some of our defending was criminal and we can’t expecting to be winning matches if we are making the mistakes that we are.”
Dover face a crucial must-win game at home to Maidenhead United on Saturday.
Hessenthaler says there are “no excuses” for such a bad display against a Magpies side who have shipped 13 goals in their last two matches.