Polow da Don and co-written in collaboration with Greg Curtis, Ester Dean and Jason Perry, "Not Myself Tonight" is an electropop, electro-R&B and dance-pop song, which explores Aguilera's adoption of different personas on the dance floor.

The single was certified gold by the Australian Recording Industry Association (ARIA) for shipments exceeding 35,000 copies in Australia.

To promote the song, Aguilera performed "Not Myself Tonight" at the 2010 MTV Movie Awards, VH1 Storytellers and The Oprah Winfrey Show, amongst others.

[2] During an interview with People in 2008, Aguilera stated that she was going to start recording new material for her forthcoming album at her home in Beverly Hills.

[13] "Not Myself Tonight" is a "straight forward", uptempo electropop, electro-R&B and dance-pop song,[14][15][16] which incorporates elements from tribal house.

[20] Eric Henderson from Slant Magazine compared "Not Myself Tonight" to Britney Spears songs "Gimme More" and "If U Seek Amy" for having similar musical style.

[22] The song also evokes sexual theme,[23] with lyrics such as "I'm dancin' a lot, I'm takin' shots and I'm feelin' fine/ I'm kissin' all the boys and girls".

[17] Writing for Billboard magazine, Michael Menachem opined that Aguilera channeled a "more 'Euro-glamorous' version" of her previous alter ego "Xtina", featured in her 2002 hit "Dirrty" from Stripped.

[20] Digital Spy editor Nick Levine gave the single a four out of five stars rating, writing that "on first listen, it feels a bit too ordinary to be trailing such a potentially audacious long-player.

"[1] Fraser McAlpine writing for BBC Music praised the song's composition yet criticized its lyrics for "[not] escaping the feeling that she's only getting up in our collective grill once again with the sexy and the [atti]'tude".

[24] Gavin Martin from the Daily Mirror wrote that "Not Myself Tonight" "shows the post-natal Aguilera has pumped up her sex appeal.

[23] Likewise, Dan Martin from NME opined that with the new musical style of Bionic and its lead single, Aguilera had very little chance to explore her vocal ability.

[28] Writing for Drowned in Sound, Richard Wink concerned that "Not Myself Tonight" showcased an "apparent identity crisis" that Aguilera experienced during the production of Bionic; he questioned whether the alter ego "Xtina" was "the character that represents a freewheeling, risk taking, carefree party girl" or the contrasting "mask a desperate popstar wears when they are struggling to maintain relevance".

[29] In his retrospective commentary on the album Bionic, Billboard's Glenn Rowley called "Not Myself Tonight" a "brashly sexual lead single".

[30] The Gay Times writer Daniel Megarry labelled the song as "an empowering feminist anthem that blended a new electropop sound with the attitude of Aguilera's Stripped era".

[32] Christopher Rosa from The Celebrity Cafe placed it at number nine on the list of Aguilera's ten best songs ever, calling it a "thumping, glittery synth sashay".

[57] The singer is seen wearing a special, glamorous eye clamps — in a scene which echoes Stanley Kubrick's dystopian film A Clockwork Orange, according to the entertainment industry-related website The Vigilant Citizen.

[54][60] MTV News' Gil Kaufman also opined that Aguilera recalled her "Dirrty" video for sharing the same sexual depiction.

[60] Tanner Stransky from Entertainment Weekly commented that the video was similar to visuals by Lady Gaga and Madonna, further noting that Aguilera "did indeed seem desperate" in the "unoriginal" clip, saying that "maybe she should have gone in a totally different direction to avoid comparisons".

[63] On behalf of Rolling Stone, Daniel Kreps stated that "Aguilera assumes no less than a dozen different guises, all scantily clad, ranging from carbon copies of Lady Gaga (borrowing heavily from her unique wardrobe), Madonna, Beyoncé, Gwen Stefani, the girls from Robert Palmer's 'Simply Irresistible' video and Michelle Pfeiffer's S&M-inspired Catwoman from Batman Returns.

[64] Idolator's editor Mike Wass opined that "the Hype Williams’ directed video is equal parts fetish porn and high-fashion shoot".

[66] Writing for the Gay Times, Daniel Megarry believed the video was a clear tribute to Madonna but "its message was lost on critics".

[75] Aguilera performed "Not Myself Tonight" on numerous occasions throughout the years, like the Justin Timberlake's all-star benefit show in Las Vegas in October 2010,[76] the Mawazine Festival in Morocco in May 2016,[77] and at the Black Sea Arena in Georgia in July 2016.

[88][89] Swiss figure skater Sarah Meier choreographed a dance routine to "Not Myself Tonight" in a show titled All That Skate.