Bipolar disorder is a mood disorder which effects a persons mood and is caused by chemical imbalances in the brain. In bipolar disorder a person has mood swings from depression to mania which have to last 7 days each to be diagnosed but generally last weeks or months at a time. I developed bipolar when I was 15 and diagnosed at 18, when I was depressed I would sleep constantly, cry, wouldn't leave bed for days, didn't eat, wash, dress, constantly felt suicidal, hopeless and worthless, withdrew myself from family and friends and stopped going to school. This lasted for 6 months. Then I switched into mania when I was constantly full of energy and felt like I was on top of the world I was so happy, didn't sleep for days and if I did I would sleep up to 3 hours only but felt completely awake and full of energy, went out every night abusing alcohol and drugs, got into meaningless relationship, had sex with strangers, had so much confidence, spent every penny I had and even stole from my mum, shop lifted, racing thoughts, aggressive and irritable, psychotic when I would hallucinate and be delusional to the point I stabbed myself and almost my boyfriend, I was constantly doing one thing to the next and I nearly failed college. This lasted for 4 months. Bipolar disorder is something that is very severe and effects your everyday life. I ended up being hospitalised because I was psychotic, hallucinating and delusional.
Borderline personality disorder (BPD) is an emotional disorder which effects a person emotions (not mood) and it is not caused by chemical imbalances in the brain but how someone has processed their emotions over time usually due to childhood trauma. Symptoms include rapid mood swings due to emotional instability, thinking in only black and white, self harm, suicidal ideation and reoccurring attempts, impulsive and/or risky behaviour, fear of abandonment, eating disorders, unstable self image and sense of self, unstable relationships with family and friends, anxiety, depression, anger and aggression. Take me as an example, I have BPD and my emotions are everywhere. I will wake up feeling so happy bouncing off the walls for no reason and then the smallest thing like not being able to turn my computer on will make me so angry and when I say angry I mean so angry I will smash my things against walls and hit my boyfriend to get all my anger out and this will last around 2 hours until I break down crying for hours just because I couldn't turn my computer on! I self harm almost every day, attempted suicide over 6 times, only think in black and white, have bad anger outbursts and switch from one emotion to the next in seconds. I also have struggled with eating disorders for 3 years and engage in risky behaviour such as drug and alcohol abuse as well as impulsively spending all my money and taking overdoses on a daily basis. I was even hospitalised for it. Because it is not a chemical imbalance the best treatment is therapy for the person to learn techniques on how to control their emotions better. Some medications can help for symptoms such as depression and anxiety but it mainly therapy that is used to help people with BPD and it is curable through therapy.
I have both these disorders. Do not self diagnose. If you think you have a mental health problem then you need to go to your doctor and explain your symptoms and ask for a psychiatric referral. A psychiatrist is the only one who can diagnose either disorder. Good luck.