22-year-old Sam will move from The Valley to Roots Hall in a bid to help Southend avoid relegation from the Championship.
He was sent out on a month's loan at
And the former England Under-20 international also enjoyed a loan spell with Leyton Orient in 2004.
The 22-year-old signed a new contract at the Valley at the start of the current campaign until 2010, but has since fallen out of favour in midfield.
Although Sam made a huge impact during Les Reed's short time as Charlton coach back in November/December, Alan Pardew is said to be not quite as "convinced" regarding the youngsters talent and was keen for him to go out on loan and prove his worth.
It also follows Tilson's wish to add some pace to the attack to help Freddy.