New research carried out on behalf of the organisation, which helps the lonely and suicidal, shows that Sunday is the day when it receives the most telephone calls from people in distress, and many of the callers are suffering from pre-Monday morning blues.
"Knowing that they have to return to the office to face the boss, or go back to school to encounter a bully, causes a great deal of distress," said Samaritans spokeswoman Emma Barton.
Sunday's unique position - on the cusp between the playtime of the weekend and the start of the working week - is the cause of its high rate of callers. Sixteen per cent of calls are made on Sunday and 32 per cent of them are taken between 10pm and 2am.
According to the Samaritans, the Sunday rush begins soon after midnight on Saturday as people return home from a night out. "They might have had too much to drink, or had a row with a girlfiend," said volunteer Paul Farmer. "It gets incredibly busy between one and three in the morning."
Later, calls pick up with those at home alone on Sunday phoning in. Their sense of isolation is heightened because many still see Sunday as a family day, and assume the rest of the world is enjoying time with their relatives, or relishing peace and quiet.
"If you are in turmoil, then the feeling that the rest of the world is enjoying tranquillity can really get to you," said Mr Farmer.
As Sunday afternoon turns to evening, different types of callers telephone. The thought of the stresses and strains of the working week tend to dominate these conversations, say the Samaritans.
"Another reason we get so many calls on Sundays is that many other organisations are shut," said Mr Farmer. "On other days, your GP would be available. But suicidal thoughts don't wait for appointments."
Last year the Samaritans received more than 3.8 million calls, of which a fifth were from first-time callers under the age of 25. Just over half were from men, who used to make far fewer calls than women.
The research into the timing of calls was carried out with the help of BT and the new national Samaritan phoneline. Since it was launched a year ago, more than 625,000 people have used it, while others have continued to use local numbers.
The volume of calls also increases at particular times of year, such as national holidays like Christmas. Calls can be made throughout the UK at any time of day. The national helpline can be phoned for the price of a local call on 0345 90 90 90.
Simon Armson, chief executive of the Samaritans, said: "As we enter the Christmas season, and some people may be feeling that their problems worsen in stark contrast with the collective cheerfulness of others, I hope that many more people may consider picking up the phone, thus relieving their sense of isolation by talking to a Samaritan who will listen in confidence and without judgement."