I worked overtime at an Amazon warehouse in the run-up to Christmas. It's like being in the gym for 10 hours straight, six days a week.

• An Amazon worker told Insider they got depressed after working six days a week before Christmas.

• The worker said after doing it for 10 weeks they "lost hope of having a normal life."

• It's "like being in the gym for 10 hours straight", they said, and working night shifts is "tough."

This as-told-to essay is based on a conversation with an Amazon warehouse worker in the UK who spoke anonymously to protect their privacy. Their identity and employment have been verified by Insider. The following has been edited for length and clarity.

My role at an Amazon warehouse is in inventory control. It involves counting how many items are placed in a bin or pod – where items are collected – scanning barcodes on items in bins, and keeping recording of how many of the same items are placed in each bin.

All of these three tasks are called counting. I also keep a record of damaged items by going around the warehouse floor and collecting them onto a trolley, entering them into a system and then sorting them.

Some of the items are sent to "damage land" – a place where we keep damaged items that can be sold at a lower price. As inventory control falls under the quality department, I also check for mistakes, such as items being put in the wrong place.

Collecting damages means having to walk all night around a huge fulfillment center. It's physically demanding because items can be heavy.

In the run up to Christmas, it's very tiring. People are stressed out and it's not a good vibe.

We get paid more money, but overtime is compulsory.

In non-peak times, I work 40 hours a week across four days. In my contract, it says that Amazon has the right to change our schedule, so when peak season starts in November, managers inform us during a briefing at the start of each shift of any schedule changes.

I was told in a briefing that it is compulsory to work five shifts a week in peak season, rather than the regular four shifts, and workers can also volunteer to do a sixth shift.