Reigning champions Liverpool are currently four points behind fifth-placed Chelsea in the Premier League
Defeat by Manchester City on Sunday leaves the Premier League champions sixth in the table - four points behind fifth-placed Chelsea.
Slot replaced Jurgen Klopp as Reds boss in June 2024 and led the club to a record-equalling 20th top-flight title in his first season in charge.
However, they have struggled this term despite spending almost £450m on new signings in the summer, including a British record £125m for Alexander Isak.
Asked by BBC Sport whether this was the toughest season he has had, Slot said: "By a mile. All the other seasons I have managed, there was only positives.
"I don't think I have ever lost two games in a row [until now]. It's an exception for me, I am not used to it.
"I don't think we feel we've only lost two of our last 17. A draw feels like a loss.
"The players know what the standards of Liverpool mean and we aren't performing to those standards. They feel that disappointment."
The likelihood is five Premier League teams, rather than the usual four, will qualify for next season's Champions League.
Last month, Slot said Liverpool would have an acceptable season if they "improve in one box" - but could have a special campaign if they "improve in both boxes".
However, on Tuesday the Dutchman suggested his side will have to be "close to perfection" to secure Champions League football next season - and he is aware of the impact of missing out.
"If we don't have Champions League football [next season], it's definitely not been an acceptable season," Slot added.
"When I arrived here and only signed Federico Chiesa, it was after a Europa League season.
"That does have an enormous impact on the way this club is run. I am completely aware of that."
Slot may be struggling for right-back options at the Stadium of Light, with Dominik Szoboszlai - who has been filling in at full-back - suspended after his late red card against Manchester City.
Conor Bradley is out for the rest of the season, Jeremie Frimpong has not featured since injuring his groin against Qarabag and Joe Gomez has been out with a knock.
Striker Isak and centre-half Giovanni Leoni are also long-term absentees.
"It's different to lead the team after a loss or multiple losses and draws than a win but I don't think anybody in this building thinks I've completely changed," Slot added.
"There's still a possibility where we can do sometime special this season."
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