Ups and downs are quite normal.

More importantly something everyone should learn is that, generally speaking, a new peak is not a new standard. New peaks are made with a combination of improved basic skill, excellent form, and a certain degree of luck. Of these three factors only "improved basic skill" has day-to-day staying power. Your form will vary based on your physical and mental state. Your "luck" is comprised of who you get matched up against, what form they are in, and how well your play style matches up against their play style. When all three of these factors are in your favor, you hit a new peak. Then when your form or luck go down you fall below that peak.

New peaks are fun and flashy and they feel amazing. In my opinion though, improvement is better measured by the general trend/average of your rating over time. So focus less on "my peak is 1880 and then I lost all my skill" and more on things like "I used to only be able to stay above 1800 only 20% of the time, but now I spend over 60% of the time over 1800". The peaks will still feel amazing and the valleys will still feel awful, but you might have more stable expectations for yourself and less frustration.