How balanced is the below spell I've created when compared to other divination or necromancy spells? Is it at the right spell level? Is it the right amount of damage/status effects?
When creating this spell, I was thinking of Contact Other Plane, Speak with Dead and Dream, and wanted to create an intersection between the three of them. The intention was to create a way to speak with long-dead, or missing, creatures, in an attempt to get information from them, with a high cost and a risk of getting hurt if you don't approach them in the right way.
The issues I've had with this spell is defining the summoned spirit in a satisfying way, as well as balancing the potential risks and damage you could get from this spell. Wording as a whole has been difficult for the spell.
A Dream of Endless Nights
6th level Necromancy (Ritual)
V/S/M (7 specially crafted black candles worth 50 gp each, which the spell consumes, and 7 humanoid skulls)
Casting time: 1 minute
Duration: 1 hour
You call on dark powers to let you speak to those long gone. When you finish casting the spell, you may speak the name of a creature that is dead. If the soul of the named creature is not free, the spell fails.
For the duration, you fall into a trance, and create a dream like environment that you can freely shape. A spirit of the creature forms in this environment. While in the trance, you are aware of your surroundings, but can't take actions or move.
The spirit is under no compulsion to answer you or to be truthful, and depending on its demeanour may be actively hostile to you.
While this spell is active, every 10 minutes you must make a Constitution Saving throw of DC 15, or take 4d6 necrotic damage as the spell steals your life essence. If the spirit is hostile to you, it can choose to force you to make this save every minute. If you fail this save, your hit point maximum is reduced by the same amount, and you gain a level of exhaustion. The reduction to your hit point maximum goes away when you next finish a long rest, and if your maximum hit points are reduced to zero by this spell then you die.
You can end the trance and the spell by concentrating for 1 minute, after which the spell ends. Once a spirit has been summoned in this way, it cannot be targeted by this spell for a year and a day.
A good answer would compare this spell to existing divination or necromancy spells.