tell them nothing. when they chase you up take 100 years to undestand who they are, just imagine you are talking to and Indian call centre, and then explain that you have terrible amnesia and must have forgotten that you have a job and that them phoning was just the best thing as now they have helped put so many pieces of the puzzle in place for you and Dr Silverman will be so pleased. Apparently it happened as you were reaching up to a high shelf for a new bottle of vodka and unfortunately some bizarre freaky twist of events meant the bottle fell and your tipple toppled onto your barnet, smashing you over the head knocking you unconscious and rendering you mental for the next 48 hours. You were found by a kindly relative who you don't remember, but your hopeful that some memories are returning. You will be back to work, hopefully as soon as the memories return, which could be next year, (boo) or within the next minute (yay) but unfortunately also the doctors have said that they could just vanish at any time in the future due to a tiny piece of glass shrapnel buried deep in your bionic implants which was too risky to remove. But should you ever not turn up for work again unnannounced, then could they kindly ring you immediately just in case it's a relapse. You might even get an orange badge for your car and be able to park right outside the establishment, they might even be able to reward you new disabled status with a small pay increment to cover and unforseen medical expenses?
Worth a try.