There are at least 7 bands named Lethargy:

1) Smooth, technical death metal from Rochester, NY. Today Is the Day, Sulaco, and Mastodon all feature alumni of Lethargy at some point.

2) Spanish electronic band with sensual female vocals. It was formed in Madrid in 1992 by Mayte Cruz and Julio Tomé.
«Hailing from Madrid, the duo Lethargy is described as a 21st century version of Massive Attack and Autechre, with a touch of Lassigue Bendthaus. A fresh mix of modern electronica with huge kicking beats and mesmerizing female vocals. Featuring sensual Spanish accented lead vocals that brilliantly contrast with the frozen electronic upbeat sequences, ''Escapa'' is a mental journey through urban ambient industrial tunes dominated by an alluring Diva. It's the ultimate clash between fire and ice, the apocalyptic distinction between cold machinery and warm seductive female whisperings.»
Metropolis, Industrial‑music.com, USA.

3) South Wales Hard/Classic Rock Grunge Band. Formed 2000. Released Debut Album 'Purification' on Classic Rock magazine's Powerage Label in Nov 2008 (Released in USA Feb 2009 via Candlelight Records).

4) Dutch Thrash‑Metal band, released one demo Anaestetic Sleep in 1988. Lethargy members formed Dead Head in 1989.

5) Dutch doom/death metal band, from the province of Friesland. Only Released 1 demo in 1999.

6) German Crust Punk/D‑beat band

7) Greek Doom/Death Metal band formed in 1996, who released a demo in 1997 and their only album in 1999.