I am a 34 year old educated single mom, my experiences started as a preteens, first ghost I saw was a grandfather that had past, I woke up in the middle of the night and he was standing there, that year it seemed quite often that my bed would start shaking but it only happened in the middle of the night, I though I would see shadowed figures quite often at that time, fast forward to young adult, I felt everyone's feelings, so much so that I had to move away from the people I was closest to because it was too much to bear I was unable to understand why I kept feeling so many emotions switching up all the time. I thought it is depression, I had a child 4 years ago since then I realized I amt extremely sensitive and now as an adult I try to make sure I protect myself from negativity because it direct instantly changes my day. Doctors say it's depression and ptsd, which I thought may have been true, until I felt pain, I felt it in the same spot on the same side where my daughter had been bitten, that night when I felt the pain I didn't realize immediately what was. Going on but in my head I said hmmm that's the same spot my baby was bitten (there was a scab left afterward), I wonder if she just pulled the scab off or scratch it. Then the other day it was super hot my aunt had her front door open and I kept seeing a dark man standing there but he would not come through the door but I knew he wouldn't come in or harm anyone, weird, again it was like my mind was telling me, then yesterday I was so worried about my cousin as soon as I woke later I found out my younger cousin's anniversary of his murder
And all in my head was my aunt's worries of her daughter who is seriously mentally ill, and family, I found out when I went to my aunt's house later! Somebody help me figure it all out, am I mentally ill or crazy!
It sounds like you're an Empath, a person that feels other people's emotions as if they're you're own. With many Empaths it goes further than just feeling emotions: they can pick up others' physical ailments as well, and anxieties, etc. Many empaths can end up anxious because of all the psychological stimuli they're receiving.
Another common issue they have is medical misdiagnosis. Because the symptoms they're showcasing can be without apparent cause (lets say they're showcasing symptoms of an ill friend but the underlying cause isn't there for doctors to find) OR during the time of the medical check up, symptoms aren't there because they're reacting to the clinic's or doctor's energy. If you relate and think you might be an Empath, consider getting a "second doctor's opinion" for whatever medical issue you'll have in your life. Misdiagnosis is very common.
Now nobody here is qualified to say if you're mentally ill...:p But let's try: Do ponies fly? How many elephants in your cupboards? Have you watched and thoroughly enjoyed any Woody Allen movies?
But seriously. Even psychic abilities or over-sensitivity can lead to things like depression if it becomes overwhelming. So I suggest you give yourself the best care available, so you can be in a positive frame of mind & enjoy your life as best you can. It'd be irresponsible to rule out depression, even if psychic abilities are simultaneously happening to you.
The ghost of your grandfather was likely real. It's a normal experience after a loved one passes away. The dark man could be anything really, it's hard to say. Based on these stories nothing points towards psychosis, congratulations, and I greatly doubt a professional would think you have a mental illness. But you sound confused and stressed over these experiences. Most Empaths are caring souls so they worry a lot. Keeping boundaries is a challenge but it's necessary.
My advice is to nurture your spirit and body. Keep observing these weird happenings. At best they can reinforce your link with your spiritual side and broaden your vision of Life. If the experiences scare you and you want them gone, reinforcing your rational side and discarding them as mere coincidences or hallucinations is OK too. Whatever keeps you strong...
In the human mind there is room for all possibilities and all skepticism. But at the end of the day it's about living life the way you want to (and can, according to your circumstances).
You might want to check out a book called The Highly Sensitive Person by Elaine N. Aron. It offers some very valuable information.
Best wishes, keep your chin up:)