Fulham were relegated last night, with three games still to play, after losing 2-0 at home to Burnley.
It means the west London club have now suffered their second relegation from the Premier League in three years.
Parker believes Fulham have a huge summer ahead of them, with talks around his future and player recruitment expected to take place once the season ends as he and the club assess why they were relegated.
"When your aim is always to grab something and be desperate for something, there are often likely scenarios of the rollercoaster that we are on at the moment," said the manager.
"We are on a rollercoaster: relegation, promotion, relegation. [Now is] not a time to talk about that really, but certainly we need to make some big decisions.
"We need to understand where we need to get to, what we need to do, where we need to improve and that's definitely going to be an area that we need to look at.
"At the moment we are going through the same cycle, so what's key is that we break that cycle and work out exactly what we need to improve as a club and move forward."
Fulham will be keen to clear up Parker's future, with their former midfielder refusing to be drawn on it after the final whistle.
Parker has been in charge since 2019 and has been linked with the vacant Tottenham job — he made 57 appearances for them between 2011-13 — and some have questioned if he will want to face another season in the Championship.
"It's not a conversation for tonight," he said. "I don't want to get involved in that. We have three games left. My job, and what I need to do, is to get this team, as disappointed as they are, to finish this season in a way which is the right way.
"After that, the discussion we have [over] what we need to do to improve will ultimately speak for itself and we will work it out from there."
One area where Fulham will have big decisions to make is around any summer signings, given seven members of their first-team squad are on loan.
Asked how important this summer will be, Parker said: "The most important, the absolute most important. We need to make some pivotal and crucial decisions to bounce back into this division."