I am going to base my advice on the fact that lexapro (us name) is the same as cipralex (european name) which I believe it is.
The recommended dosage for people who have suffered panic attacks is to start at one 5mg per day for the first week and then increase to one 10mg per day in the second week. This is because these tablets can initially cause an increase in anxiety if you start on too high a dosage.
This gradual increasing of dosage is what I have done and I have suffered no side effects of any note. I took the 5mg half-tablets for the first week and then upped my dosage to the 10mg. I am have been on the 10mg tablets for 15 days now and am doing well. I take my tablet in the morning about 30mins after breakfast (it's good to take these tablets with food to minimise any stomach upset). But you should follow your doctor's advice on when to take them. If he told you to take them before bed then stick with that.
I hope this has helped, take care...