Caz23, thanks for your question. When someone suffers from depression, their lives are altered in many ways, which not only affect the sufferer but also to a degree, those around them who care about them. Emotional state, attitude, decision making and reasoning is altered, which can, in certain situations, have sad consequences for themselves as well as their family or friends.
The fact that you ask about the warning signs, may be an indication in itself that asking for more information and perhaps for advice from your own GP, could prove beneficial. I'm certainly not saying that you may have depression, not at all, just that if you feel you may have some symptoms, talking to someone about it is the first step in overcoming depression.
Men particularly, choose not to talk about their depression symptoms or actively seek help for their condition, because of a perceived stigma associated with depression, this is increasingly changing however, with greater awareness and acceptance by the community. So, no-one has to suffer in silence, there is lots of help and effective treatment available from General Practioners, organizations and online websites if needed.
As mentioned by NateSean, the altered state of a sufferer can have other potentially dangerous consequences too. All reasons to actively seek out some form of assistance and treatment and ultimately a cure for the condition. Hope all is well with you Caz and I wish you all the best.