If the January blues have already taken a firm hold, the perfect tonic is to book your summer holiday.  And you could be sealing the deal sooner than you thought, as Aer Lingus has just announced a massive sale, running until 18th January and applying to flights from May 1st to September 30th. The "Tick All The Boxes" summer sale has slashed fifty per cent off all flights from Ireland to European destinations. That means you can nab flights to Britain for as low as €19.99 each way and flights to North America are as low as €255 each way, according to the Irish Mirror.  Flights must be booked before midnight on January 18th. Speaking about the sale, Chief Commercial Officer of Aer Lingus Keith Butler said: "The first few days back at the desk in January are when people are daydreaming most about being on their summer holidays and in 2016, Aer Lingus is offering more choice and great value fares to Europe, North America and the UK. "For summer, we’ve introduced new routes from Dublin to Murcia, Pisa and Montpellier and to North America; Los Angeles, Newark and Hartford, Connecticut. "In 2015, a staggering 6 billion kilometres were travelled during the summer months, June through to the end of August, and with wanderlust at an all-time high, we expect to surpass this in 2016." What are you waiting for? Go, go, go.