It depends on how old she is. If she’s particularly young, this is actually rather normal behavior. However, it can and should be corrected to maintain her mental health. This behavior tends to be unusual in older pokémon (generally speaking), especially if it’s sudden. If your mawile is older and this behavior has only recently started, it’s imperative that you rule out other causes of stress before proceeding. As I’ve mentioned a few times on this blog, sometimes a new move or a new teammate can cause extreme stress, and it’s up to the trainer to reassure their pokémon that all is well. Alternatively, she may be trying to tell you that something is legitimately wrong with your home—as in, there is a legitimate threat—so it may be prudent to check for any specific behaviors (or behaviors that indicate that she is reacting to something specific).
If your mawile is most definitely suffering from separation anxiety, regardless of whether your mawile’s case is mild or severe, counterconditioning and desensitization are the keys to helping her stability.
Begin by establishing a routine for leaving. Whenever you leave the house (or even her sight), give mawile a clear cue that you need to go temporarily. This can be as simple as jingling your keys, or it could be as direct as telling her, “Mawile, I’ll be back soon.” Once she associates that cue with your leaving, she’ll be able to anticipate these absences.
Additionally, give your mawile an item of yours (such as a worn piece of clothing or something she would associate with you) to remind her of you in your absence. It may also help to take the object back when you return so your mawile will be able to associate the act of you giving her an item with a temporary leave. She will, in other words, begin to see this act as a sign that you will be back for this item—and, by extension, her.
Don’t just give her an item of yours, either. Also give her a toy or leave out a treat. If you leave something just for her, then she’ll also associate your absences with something good, and thus, she’ll be more likely to relax and even look forward to them.
Of course, you’ll also want to use positive reinforcement with all of this as well. Whenever you come home to find that she took your absence well (or comparatively calmer than she is right now), give her a treat. The more you do this, the more you can train her to understand that your absences are not a bad thing.
Finally, above all else, do not start by leaving her for hours on end. Use the above steps on even minor separations. For example, if you need to spend a few minutes in another room but don’t want her to follow, give her a cue, a toy, and a token, then give her a treat if she takes it well. Once she’s able to handle a few minutes, proceed to leave her alone for an hour, then a few hours, then for a full workday. Likewise, increase your time away from her more and more, even if the problem is just that she refuses to reenter her poké ball for fear of being separated from you. Until she can handle longer periods of time away from you, you will still need to take her with you wherever you go or leave her in the care of someone she trusts. As with helping to relieve stress in any pokémon, it will take time, patience, and the right amount of care and reassurance to help her.
Good luck, anonymous.
The Pokédex According to Bill 