If your spouse just recently broke the news of a separation to you, or you are still coming to terms with the decision, you should probably wait before talking to the kids. You'll want to be able to emotionally support your kids, depending on their reaction. Doing so will be a challenge if you're still a wreck yourself. Ask for some time and/or space before having the talk. You might say, "Is it okay if you give me a week before we tell the kids? I need to wrap my head around this first." In the meantime, lean on friends and family. Be gentle with yourself as you come to terms with the separation. Both parents should present as a united front. Therefore, you need to be clear about what you're telling the kids. Have a discussion beforehand about the details. Once the two of you have agreed on what you'll say, stick to the script. For instance, you might say, "Your father and I are going to separate." Your spouse can follow up by saying, "We aren't getting along anymore." Then, echo one another by both letting the child know, "We love you." It will be confusing if you break the news to the children on your own. They need to see you and your spouse working together as a reminder that you are both still their parents. That much, at least, hasn't changed. Coordinate with your spouse on a time and place to schedule the talk. Pick a time when you're both free and relatively relaxed. Clear the remainder of your day or evening, so you can offer reassurance or support to the children as needed. Also, if the separation isn't happening for some time, you might choose to delay the discussion until closer to the planned date. Otherwise, the children might become confused and think it's no longer happening. If one of the parents is unable or unwilling to participate in this conversation, try to remain as objective as possible. Do not badmouth the other parent. Just stick to the facts.
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One-sentence summary -- Gain control of your emotions first. Get on the same page. Plan to do it together.

This is most common dangerous and powerful drugs like heroin. Downers, like opiates, usually leave people in a happy stupor, unable and unwilling to move off the couch they're on. They often squirm around sensually like a baby in blankets, getting comfortable and enjoying every single second of it. Watch Ewan McGregor's masterful performance as a heroin addict in Trainspotting to see how quick this shift can be. Opiates often hit hard, bringing a wave of euphoria, before putting the user into a mellow, sleepy, and often useless state. Most opiate users have their heads blissfully in the clouds. They may start a thought, but finishing it isn't really important. Ask someone's attention, but don't have anything to say when they turn to you. Keep your voice low and quiet. The overall idea is to remain stuck in the clouds, unable to pin down your thoughts. More often than not, this leads to literally falling asleep, your head lolling up in surprise slightly every so often, as if just waking up. Again, this is particularly true of heroin, but drugs like Oxycontin are actually the same type of compound, just slightly weaker. Scratch on your forearms, but don't make a big deal of it. This is just another uncontrollable tic, not some dedicated urge.
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One-sentence summary --
Act like a sleepy, happy baby, talking little and smiling sleepily. Lurch into wide-eyed happiness right after "taking" the drug, then fade into sleepiness. Let your words and actions drift off into nothing. Drift off regularly, either by falling asleep or simply zoning out into oblivion. Scratch at yourself regularly, as itchiness is often a side-effect of opiates.